The equations of motion are
The normal mode frequencies are found by setting
which can be written in matrix form
There is a non-trivial solution for , , and if and only if the matrix
has zero determinant. Upon setting the determinant equal to and solving the resulting equation for , one will presumably find that is a solution. Plug into equation (16) and solve for , , and . This leads to
which means that the motion corresponding to this normal mode is given by
The statement that describes this motion is . Therefore, answer (B) is correct.