Hi mukherjee.tanuj3,
This SC is built on Comparison and Modification rules:
1) Comparison - the word "unlike" at the beginning of the sentence tells us that we'll have to compare similar things that differ in some way. 3 of the answers make an improper comparison:
Answer A: compares "many routine tests" with "many newly discovered genetic defects"
Answer B: compares "diabetes or high cholesterol" with "tests"
Answer C: compares "diabetes or high cholesterol" with "tests"
Answer D: compares "routine tests" with "tests"
Answer E: compares "routine tests" with "tests"
Eliminate A, B and C
2) Modification - the "tests" are what cost money, not "the diseases". Eliminate E.
Final Answer: D
GMAT assassins aren't born, they're made,
Rich