Answer:
Your answer would be A.
Explanation:
You should change suns' to sun's. You should use the apostrophe to show possession. In order to show possession with a singular noun, you should add an apostrophe plus the letter -s. As you know, the sentence is referring to the sun, the star of our galaxy. Considering that the noun is singular (sun), the possession should be shown by adding the apostrophe and the letter -s to the noun (see 1).
1) The sun's energy heats the Earth's surface
