If two vectors are parallel to each other, then the magnitude of cross product of two vectors is

If two vectors are parallel to each other, then the cross product of two vectors is zero.

So B,C,D are not correct.

If two vectors are parallel to each other, the angle between them is 0° then

$\overrightarrow{a}\times \overrightarrow{b}=\text{ab\hspace{0.17em}}\sin \theta =\text{ab}\sin 0°=0$