Hi Satish,(Let me help you out with assumption questions..!!)
All CR questions in GMAT are flawed. Read each of the questions with an intent to identify the flaw. All questions contain atleast one premise and atleast one conclusion. One key point to getting CR questions right is identifying the two. There is can be multiple premises and multiple conclusion. But the idea is to summarize the complicated information into one sentence. Follow the below steps:
1) Break down each sentence into background information, Premise, Conclusion.
(Background information -- is information sets up the scenario for the premise and conclusion to happen)
2) Summarize the Argument core: Premise ---> Conclusion.
3) The answer choices given should fill the blank between the premise and conclusion. These are assumptions that the author has assumed for the conclusion to be valid
4) Use negation test-- Negate each of the answer choices and place it between the premise and conclusion. The argument core doesnt hold valid for the correct answer.
Hope this helps.!! Let me know incase you have any further queries.