Questions: If a line segment from two points on the circumference of a circle passes the center, it is called the diameter

The answer is the third one: the diameter.

Explanation for each option:

1. The radius: This is incorrect. The radius is a line segment from the center of the circle to any point on the circumference, not a line segment that passes through the center connecting two points on the circumference.

2. The ellipse foci point: This is incorrect. The foci are specific points related to ellipses, not circles. This term does not apply to a line segment in a circle.

3. The diameter: This is correct. The diameter is a line segment that passes through the center of the circle and has its endpoints on the circumference. It is the longest possible line segment that can be drawn within a circle.

4. Not possible: This is incorrect. It is indeed possible for a line segment to pass through the center of a circle and connect two points on the circumference; this is known as the diameter.

In summary, the correct term for a line segment that passes through the center of a circle and connects two points on the circumference is the diameter.