Mark against the correct answer in each of the following:

Mark $(\sqrt{ })$ against the correct answer in each of the following:

If $\vec{a}, \vec{b}$ and $\vec{c}$ are mutually perpendicular unit vectors then $[\vec{a}+\vec{b}+\vec{c}]=$ ?

A. 1

B. $\sqrt{2}$

C. $\sqrt{3}$

D. 2