When the moon size is half of the full moon, the angle between the Sun, the Earth and the Moon is

The correct answer is (c).

When the moon size is half of the full moon, it is called a quarter moon. A quarter moon occurs when the moon is 90 degrees from the sun in the sky. This means that the sun, the earth, and the moon are in a straight line, with the earth in the middle.

Option (a), 45 degrees, is incorrect because the moon would be too close to the sun to be visible. Option (b), 90 degrees, is correct because the moon is 90 degrees from the sun in the sky. Option (d), 270 degrees, is incorrect because the moon would be on the opposite side of the earth from the sun.