Let V be the (real) vector space of all functions f from R into R. Which of the following sets of functions are subspaces of V?
(a) all f such that f(x2)=f(x)2;
(b) all f such that f(0)=f(1);
(c) all f such that f(3)=1+f(−5);
(d) all f such that f(−1)=0;
(e) all f which are continuous.