$\displaystyle\mathbb{R}^n=\bigcup_{k=1}^\infty W_k$

Question

Show that if $\mathbb{R}^n=W_1\bigcup W_2\bigcup\ldots\bigcup W_k\bigcup\ldots$, where each $W_k$ is a subspace , then $\mathbb{R}^n=W_i$ for some $i$.