Which of the following sets are subspaces of ${\mathbb R}^3$?

A. $\{ (-3, y, z) \ | \ y, z$ arbitrary numbers $\}$
B. $\{ (-8 x + 2 y, -9 x - 6 y, -5 x + 6 y ) \ | \ x,y$ arbitrary numbers $\}$
C. $\{ (x,y,z) \ | \ -3 x + 7 y - 4 z = 0 \}$
D. $\{ (x,y,z) \ | \ 9 x + 5 y - 2 z = 8 \}$
E. $\{ (x,y,z) \ | \ x, y, z > 0 \}$
F. $\{ (x, 0, 0) \ | \ x$ arbitrary number $\}$