The answer is (c)sin0

remember the following so you wont get confused

A) trig functions + reciprocal trig functions
sin x = \frac{1}{csc x}                        csc x = \frac{1}{sin x}
cos x = \frac{1}{sec x}                       sec x = \frac{1}{cos x}
tan x = \frac{1}{cot x}                         cot x = \frac{1}{tan x}

B) Quotient Identities
tan x = \frac{sin x}{cos x}                    cot x = \frac{cos x}{sin x}

C) Pythagorean Identities
sin^2 x + cos^2 x =1
1 + tan^2 x = sec^x
1 + cot^2 x = csc^2 x

there are also half angle identities, etc. but those 3 above should be enough for now