suchit wrote:I'm still not clear as to how C is the answer as the question does not give any relation between A and D, therefore I thought that the answer should be B.
It does give a relationship between A and D, as loki.gmat explains above. The question says 'If A is true, then B is true'; 'If B is true, then C is true'; 'If C is true then D is true'. Taken together, this means 'If A is true, then D is true'. If this weren't the case, we would not be able to solve equations that have several steps. Take a question where you are asked to find x^2:
x = 2x - 4
A
4 = 2x - x
B
4 = x
C
16 = x^2
D
there is certainly a relationship between A and D here: if A is true, then B is; if B is true, then C is; if C is true, then D is. Thus, from A, we conclude that D is true. Notice also that some steps are not reversible here. If D is true, that does not mean that C is true; x might be negative 4, not positive 4.
The Critical Reasoning question in the original post tests whether you understand what is known as the 'contrapositive' in mathematical logic. Whenever you know: 'If A is true, then B is true', you can always conclude: 'If B is false, then A is false'. You cannot, however, reverse the statement- If B is true, you cannot be sure that A is true.
So, A might be 'it's raining', and B might be 'there are clouds'. It is true that 'If it's raining, there are clouds'. You cannot simply reverse the statement- you cannot necessarily conclude 'If there are clouds, it's raining'. We know that's false. You can, however, reverse the statement
and make A and B false: 'If there are no clouds, it's not raining'. This is the 'contrapositive' of the original statement, and is always a valid logical deduction.
Aha - Got it. Thanks for your detailed reply
