If 0 < st < 1 then which of the following can be true?

Let's examine each answer choice.....

(A) s < -1 and t > 0
This tells us that s is NEGATIVE and t is POSITIVE, which means the product st must be NEGATIVE
We're told that 0 < st < 1, which means st is POSITIVE
Eliminate answer choice A

(B) s < -1 and t < -1
This tells us that s is NEGATIVE and t is NEGATIVE , which means the product st must be POSITIVE
We're told that 0 < st < 1, which means st is POSITIVE (so far good!)
However, if s < -1 and t < -1, the product st will be GREATER THAN 1, and we're told that st is LESS THAN 1
Eliminate answer choice B

(C) s > - 1 and t < -1
So, it COULD be the case that s = -0.5 and t = -1.2, in which case st = (-0.5)(-1.2) = 0.6
Perfect! [since it is true that 0 < 0.6 < 1]

Answer: C

Cheers,
Brent