Conventionally the direction of current is taken as

The direction of the current may be observed from two distinct angles: one is by looking at the flow of positive charge, and the other is by looking at the flow of negative charge. Electric current itself is a kind of charge flow, hence charge is taken into account. To find the correct response, use this idea.

Conventionally, the flow of positive charge from the source's positive terminal into the source's negative terminal is thought to be the direction in which current flows.
It is only a convention; the direction used to describe the flow of current in electrical circuits is not the actual direction of the current.
Therefore, traditionally, the flow of positive charge is assumed to be moving in the direction indicated by the current, as in the picture.

Hence option D is the correct answer.