D. straight line motion
A wave travels in circular motion/irregular motion/vibrating motion when the medium is non-uniform or there is unbalanced force acting on it.
when the medium is uniform, the wave would continue to travel in the straight path and would not deviate. A light wave always moves in straight path in a given medium. It bends when the medium changes.
t. w e n t y c h a r a c t e r s
a. irregular motion<...