Multiple choice question [urgent]

Hello guys, I need help with this multiple choice question. I am thinking the answer is A but I am not sure.

Over a period of just fifteen years ending in 2006, the mountain pine beetle has killed an
estimated twenty millions acres of trees in the Rocky Mountains of British Columbia.
These dead trees, in addition to no longer photosynthesizing to remove CO2 from the
atmosphere, will actually emit it during their decomposition. As of 2013, the mountain
pine beetle has since killed about 50% of the total volume of commercial lodgepole pine
in BC.

The beetles, and a fungus with which they are often infected, together damage the xylem
cells, which causes

A) an inhibition of photosynthesis.
B) a disruption of the Calvin cycle.
C) a blockage of water transport.
D) an inhibition of respiration.