The sun always shines directly overhead at noon. This is because the equator always gets the equivalent amount of sunlight. The area always get 12 hours of sunlight, because it's 0 degrees north and south and it's at the center of the Earth.
Choice C.
That's when convection stops.
For pressurized water reactors the coolant is not permitted to boil in the core of the PRW, however the coolant in boiling water reactors is permitted to do so in the core of BWR. Pressurized water reactors have an indirect cycle. Whereas, the boiling water reactors go through a direct cycle. Both are light water reactors.