Let ${\bf u}_4$ be a vector that is not a linear combination of $\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3\right\rbrace$.

Select the best statement.

A. There is no obvious relationship between span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3\right\rbrace$ and span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3,{\bf u}_4\right\rbrace$ .
B. span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3\right\rbrace=$ span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3,{\bf u}_4\right\rbrace$ when ${\bf u}_4$ a scalar multiple of one of $\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3\right\rbrace$.
C. We only know that span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3\right\rbrace\subseteq$ span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3,{\bf u}_4\right\rbrace$.
D. span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3\right\rbrace\ne$ span$\left\lbrace{\bf u}_1,{\bf u}_2,{\bf u}_3,{\bf u}_4\right\rbrace$.
E. none of the above