Which function's graph has a period of 2?

A. y=cos (x-pi/2)

B. y=3cos pi x

C. y=2 sin 3x

D. y=-4 sin 2x

Given that the function is:

y=a cos (bx+c), or y=a sin (x+c)

then the period is calculated as T = 2π/b and if T=2:

2=2π/b

b=2π/2=π

Therefore, the correct answer is option B, y=3 cos πx.

Hope this answers the question. Have a nice day.