moderator, please move this question to DS section.
C.

I: a-b<0 & a+b<0 =>a<0. can't say anyhting about b. INSUFFICIENT.
II: exactly one of a and b is negative. INSUFICIENT.

Both: a is negative, so b is positive.

varunkh70 wrote:14) a-b < 0. Is b<0?

1)a<-b
2)ab<0

i got B, my reasoning
if a<b, is b<0
(1) insufficient as it gives us only a<0, and so b can be +ve, or -ve
(2) two cases are possible
a>0, b<0
a<0, b>0

if a>0 then according the condition that b>a, b must be +ve, but it is not possible as if a>0, b must -ve
so left with 2 case where
a<0, and b>0
so B

varunkh70 wrote:14) a-b < 0. Is b<0?

1)a<-b
2)ab<0

We know from the stem that a < b. The question is asking whether b is negative.

(1), as the previous poster points out, gives us no info about b's sign. Insufficient.
(We know that a < b, and that a < -b. We still don't know b's sign though. Whatever b's sign is, all we know is that there is some number, "a", that is smaller than both the positive and negative "version" of another number, "b", and so "a" must be negative).

(2), also as the previous poster points out, means that "a" and "b" have different signs. So, if "b" were negative, then "a" would be positive. But this would violate info in the question stem (a < b). So, "b" can't be negative. Sufficient.

Choose B.