Let h be the set of all vectors of the form <-7t, 2t, 4t>. Find a vector v in ℝ³ such that h=span{v}. Why does this show that h is a subspace of ℝ³?

a) <1, 1, 1>
b) <-7, 2, 4>
c) <0, 0, 0>
d) <7, -2, -4>