Answer:
Option A is true
Step-by-step explanation:
Consider a right triangle ABC right angled at B.
Then we have A+C=90 since sum of all 3 angles =180
A and C are complementary
A has opposite side as BC and hypotenuse as AB
sin A = BC/AB
Consider angle B.
B has adjacent side as BC and hypotenuse as AB
So cos B = BC/AB
i.e. sin A = cos B
Hence we have option A to be true.