Answer:
 D. I and IV only
Step-by-step explanation:
You want to know which of the trig functions have asymptotes at x = nπ for integers n.
Vertical asymptotes
The trig functions with vertical asymptotes at x = nπ will be those that can be written equivalent to something with sin(x) in the denominator. Sin(x) is zero for x = nπ, so that will make 1/sin(x) have vertical asymptotes at those values of x.
 I. csc(x) = 1/sin(x) . . . . . has vertical asymptotes at x=nπ
 II. cos(x) . . . . is always finite; no asymptotes
 III. tan(x) . . . . has vertical asymptotes an π/2+nπ
 IV. cot(x) = cos(x)/sin(x) . . . . . has vertical asymptotes at x=nπ
The correct choice is I and IV only.