Which function has an asymptote at x=pi/2?

a) y= sec x

b) y= cot x

c) y= csc x

d) y= cos x

This is what i found “an explicit formula designates the nth term of the sequence, as an expression of n (where n = the term's location). it defines the sequence as a formula in terms of n. this example is an arithmetic sequence(the same number, 5, is added to each term to get to the next term).” i hope this you for what your looking for. can you plz mark me brainliest?