中国大学MOOC: In euphotic zone (真光层), which of the following is correct?

In euphotic zone (真光层), which of the following is correct? A: The photosynthesis of phytoplankton is stronger than respiration B: The photosynthesis of phytoplankton is weaker than respiration C: The photosynthesis of phytoplankton is the same as respiration D: All the answers are incorrect