aditya8062 wrote:In some species of Cricket, the number of chirps per minute used by the male for attracting females rise and fall in accordance with the surrounding temperature, and they can in fact serve as an approximate thermometer

A. for attracting females rise and fall in accordance with the surrounding temperature, and they can in fact serve
B. for attracting females rises and falls in accordance with the surrounding temperature, which can in fact serve
C. in attracting females rise and fall in accordance with the surrounding temperature, in fact possibly serving
D. to attract females rises and falls in accordance with the surrounding temperature, and it can in fact serve
E. to attract females rises and falls in accordance with the surrounding temperature, in fact possibly serving

my concern : i can understand as why E is wrong but somehow i am not able to appreciate the presence of "and" in option D

D says: to attract females rises and falls in accordance with the surrounding temperature, and it can in fact serve.

i believe that "AND" connects two independent ideas which are equal in priority and unless there is a transition word these two ideas are independent of each other .also if are putting two things in parallel with "and" then we should be able to talk about those two things as A and B OR as 1 AND 2 .

However in option D the construction after "AND" is very much an extension of the idea of previous clause and hence nothing of the sort (as described above in italicized) is happening in option D

First action: The number of chirps rises and falls.
Second action: The number of chirps CAN serve as an approximate thermometer.
These two actions are not contemporaneous but are DISCRETE.
The number of chirps does not actually serve as a thermometer when it rises and falls.
Rather, the number of chirps has the POTENTIAL to serve as a thermometer.
Since the two actions are discrete, the OA connects them with and.

Also, the structure of the sentence is as follows:
INTRODUCTORY MODIFIER + INDEPENDENT CLAUSE + AND + INDEPENDENT CLAUSE.
In this structure, the introductory modifier refers only to the first independent clause.
In the SC above, one purpose of and is to make it clear that the introductory modifier (in some species of cricket) does NOT serve to modify the second clause.
The following sentence would not convey the intended meaning:
In some species of cricket, the number of chirps can serve as an approximate thermometer.
While the number of chirps can serve as a thermometer FOR US, it does not serve as a thermometer in some species of cricket.

Another example of this structure in the OG12:
Long before it was fashionable to be an expatriate, Josephine Baker made Paris her home, and she remained in France during the Second World War as a performer and an intelligence agent for the Resistance.
Here, the introductory modifier (highlighted in red) serves to modify only the first clause: how Josephine Baker MADE PARIS HER HOME.
It does not serve to modify how Josephine REMAINED IN FRANCE DURING THE SECOND WORLD WAR.

question 2 : also please tell me if the modified E would be correct ?

modified E : to attract females rises and falls in accordance with the surrounding temperature, possibly serving

Best

As noted above, the number of chirps is not actually serving as thermometer when it rises and falls, so this modified version of E is not viable.