Critical Reasoning

Astronomer: Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique, homogeneous chemical composition. Therefore, whenever to stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Which of the following, if true, would most strengthen the astronomer's argument?

a) In some groups or stars, not every star originated from the same parent cloud of gas
b) clouds of gas of similar or identical chemical composition may be remote from each other.
c) Whenever a star forms, it inherits the chemical composition of its parent cloud of as
d) Many stars in vastly different parts of the universe are quite similar in their chemical compositions
e) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.

Answer [spoiler]D, which surprises me, because I thought in Strengthen questions there's supposed to be NEW information, however, D simply repeats information that is already in the passage. Is my thinking wrong here??[/spoiler]

dqure040 wrote:Astronomer: Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique, homogeneous chemical composition. Therefore, whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Which of the following, if true, would most strengthen the astronomer's argument?
a) In some groups or stars, not every star originated from the same parent cloud of gas
b) clouds of gas of similar or identical chemical composition may be remote from each other.
c) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas
d) Many stars in vastly different parts of the universe are quite similar in their chemical compositions
e) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.

Premise: Each parent cloud has a unique, homogeneous chemical composition.
Conclusion: Stars with the same chemical composition must have originated from the same cloud of gas.

This CR links the chemical composition of STARS to the chemical composition of the PARENT CLOUD.
Only C strengthens this link:
Whenever a STAR forms, it inherits the chemical composition of its PARENT CLOUD of gas.

The correct answer is C.

The problem above is CR2 in the OG16.
In the OG16, the OA is not D but C.

GMATGuruNY wrote:

dqure040 wrote:Astronomer: Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique, homogeneous chemical composition. Therefore, whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Which of the following, if true, would most strengthen the astronomer's argument?
a) In some groups or stars, not every star originated from the same parent cloud of gas
b) clouds of gas of similar or identical chemical composition may be remote from each other.
c) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas
d) Many stars in vastly different parts of the universe are quite similar in their chemical compositions
e) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.

Premise: Each parent cloud has a unique, homogeneous chemical composition.
Conclusion: Stars with the same chemical composition must have originated from the same cloud of gas.

This CR links the chemical composition of STARS to the chemical composition of the PARENT CLOUD.
Only C strengthens this link:
Whenever a STAR forms, it inherits the chemical composition of its PARENT CLOUD of gas.

The correct answer is C.

The problem above is CR2 in the OG16.
In the OG16, the OA is not D but C.

Can you explain more about the Choice E and OG's explanation of Choice E?
Thanks in advance!

Crystal W wrote:Can you explain more about the Choice E and OG's explanation of Choice E?
Thanks in advance!

The astronomer is saying that since the gas clouds that stars form from have a unique chemical composition, stars with the same chemical composition must have formed from the same cloud of gas.

What the astronomer is saying seems logical but may be incorrect, as it could be the case that the chemical composition of stars is somehow not entirely connected to the chemical composition of the parent gas cloud of the stars. For instance, the chemical composition of a star could be affected by factors other than the chemical composition of the parent cloud of gas.

E is a tempting answer in that if astronomers can tell whether a star has the same chemical composition as its parent cloud of gas, they may find support for the conclusion of the argument. If they were to find evidence that indicates that all stars have the same chemical compositions as their parent clouds, then that evidence would support the argument that sets of stars that come from a particular cloud share a unique chemical composition, that of the parent cloud of that set of stars.

That's great, but notice the following. E only says that the astronomers CAN DETERMINE WHETHER the stars have the chemical composition of their parent clouds. It does not say WHAT THEY DETERMINE. For all we know, when they make a determination, they determine that the stars do not have the same chemical composition as their parent clouds of gas.

Since E does not say what the scientists determine, it neither supports nor weakens the argument. It indicates that scientists COULD find evidence to support, or weaken, the argument but does not say that they do or what they find.