The consistent mass matrix of a bar element is given by

a. \(\frac{ho A l}{6}\left[\begin{array}{ll}2 & 1 \\ 1 & 2\end{array}\right]\)

b. \(\frac{ho A l}{6}\left[\begin{array}{rr}2 & -1 \\ -1 & 2\end{array}\right]\)

c. \(\frac{ho A l}{6}\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right]\)