hello all!

i have a question here..its an exercise question from the usingz book. the question is:

We may categorise functions of

{0; 1} -> {0; 1} according to whether they are injective, surjective both. State functions which are:

(a) total functions

(b) injective but not surjective

(c) surjective but not injective

(d) bijective

for this question, how do i answer it? i don't understand wht the question is asking for. thanks in advance!!