Change of velocity takes place

Change of velocity takes place we get following are true.

i) Even when magnitude of velocity changes

ii) Even when direction of velocity changes

iii) Even when both magnitude and direction of velocities changes.

But direction of change of velocity will be along vector difference of final and initial velocities.

$\mathrm{\Delta }\overrightarrow{\mathrm{v}}=\overrightarrow{{\mathrm{v}}_{\mathrm{f}}}-\overrightarrow{{\mathrm{v}}_{\mathrm{i}}}$

So we get a, b and c are true.