In Japan, the Presence of Ducks and the Aquatic Fern

In Japan, the presence of ducks and the aquatic fern Azolla in rice cultivation has shown that ____________.

A) ducks and other birds must be eliminated from rice fields
B) GM crops such as rice cannot succeed without ferns to provide shade and ducks to provide pollination
C) the ferns provide an excellent food for ducks
D) restoring portions of the biodiversity of a natural ecosystem increases crop yields and profits
E) invasive species diminish rice yields