Mathematics

Problem

\vec{p}\times\vec{q}=\vec{0}

and neither

\vec{p}

nor

\vec{q}

is the zero vector, the angle between

\vec{p}

and

\vec{q}

is a)

90^{\circ}

0^{\circ}\text{ or }180^{\circ}

180^{\circ}

0^{\circ}