The lumped-mass matrix of a bar element is given by

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

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

c. \(\frac{ho A l}{2}\left[\begin{array}{ll}1 & 0 \\ 0 & 1\end{array}\right]\)