Which sentence below correctly refers to the collective noun troop as a whole unit?
A. The troop are marching down the hill to a shady spot to rest.
B. The troop is marching down the hill to a shady spot to rest.
C. The troop are planning to change their shoes while they rest.
D. The troop have to raise at least $500 each in order to be able to attend summer camp this June.
