Question:
If pqr = 1 , rst = 0 , and spr = 0, which of the following must be zero?

Option A):
p
Option B):
q
Option C):
R
Option D):
S

Correct Answer is Option D):
S

Explanation:
If pqr = 1, none of these variable can be zero. Since spr = 0 , and since p and r are not zero, s must be zero. (Note that although rst = 0, and so either s or t must be zero, this is not sufficient to state which must be zero)