Answer: A. Ray
Explanation:
A ray is a part of a line that starts at a fixed point and goes towards in a particular direction to infinity where as a line has no endpoints such that it goes towards infinity from both the sides.
The point where the ray begins is known as its endpoint.
Similarly as a line, ray passes through infinite points on its way in a particular direction .
Thus, the basic geometric term can be called "half of a line" is ray.