If the directions cosines of a line are $k,k,k$ then

Question

$$(A)\;k\;>\;0\qquad(B)\;0\;<\;k\;<\;1\qquad(C)\;k\;=\;1\qquad(D)\;k\;=\;\frac{1}{\sqrt 3} or \frac{-1}{\sqrt 3}$$