Critical Reasoning

naaga wrote:Increase in the level of high-density lipoprotein (HDL) in the human bloodstream lower
bloodstream-cholesterol levels by increasing the body�s capacity to rid itself of excess cholesterol. Levels of HDL in the bloodstream of some individuals are significantly increased by a program of regular exercise and weight reduction.
Which of the following can be correctly inferred from the statements above?
A. Individuals who are underweight do not run any risk of developing high levels of cholesterol in the bloodstream.
B. Individuals who do not exercise regularly have a high risk of developing high levels of cholesterol in the bloodstream late in life.
C. Exercise and weight reduction are the most effective methods of lowering bloodstream cholesterol levels in humans.
D. A program of regular exercise and weight reduction lowers cholesterol levels in the bloodstream of some individuals.
E. Only regular exercise is necessary to decrease cholesterol levels in the bloodstream of individuals of average weight.

When answering inference questions on the GMAT, are looking for the answer choice that MUST follow from the premises. So, as we examine the answer choices, we must aggressively eliminate any answer choice that does not necessarily follow from the premises.

(A) Individuals who are underweight do not run any risk of developing high levels of cholesterol in the bloodstream.
The passage says that SOME people on a weight reduction program may see increased levels of HDL. This does not mean that underweight people will NEVER have high levels of cholesterol.
Eliminate answer choice A

(B) Individuals who do not exercise regularly have a high risk of developing high levels of cholesterol in the bloodstream late in life.
There is nothing in the passage that guarantees this to be true. All we are told is that SOME people who exercise may see increased levels of HDL. We are not given any information about people who do NOT exercise.
Eliminate answer choice B

(C) Exercise and weight reduction are the most effective methods of lowering bloodstream cholesterol levels in humans.
The MOST EFFECTIVE? This language is too strong. All we are told is that SOME people who exercise and are on a weight reduction plan may see increased levels of HDL. That's it. There's nothing here that says this is the BEST way to reduce cholesterol.
Eliminate answer choice C

(D) A program of regular exercise and weight reduction lowers cholesterol levels in the bloodstream of some individuals.
Notice how the language in this house for choice matches the language in the passage. In the passage we are told that SOME people see lowered cholesterol levels. This answer Choice also uses the limiting word SOME.
Keep answer choice D

(E) Only regular exercise is necessary to decrease cholesterol levels in the bloodstream of individuals of average weight.
ONLY regular exercise??
This language is too strong also. The passage tells us that SOME people who regular exercise will see decreased levels of cholesterol. There is nothing in the passage that suggests that regular exercise is the ONLY way to decrease levels of cholesterol.
Eliminate answer choice E.

By the process of elimination the correct answer is D.

Cheers,
Brent