Which of the following subsets of $P_2$ are subspaces of $P_2$?

A. $\{ p(t) \ | \ p'(t) + 4 p(t) + 8 =0 \}$
B. $\{ p(t) \ | \ p'(t)$ is constant $\}$
C. $\{ p(t) \ | \ p(2)=6 \}$
D. $\{ p(t) \ | \ p'(5)=p(7) \}$
E. $\{ p(t) \ | \ p(-t)=-p(t)$ for all $t \}$
F. $\{ p(t) \ | \ \int_0^{8} p(t)dt = 0 \}$