23. Biochemists use fireflies to study bioluminescence, _____
(A) the heartless light given off by certain plants and animals.
(B) certain plants and animals give off the heartless light.
(C) that certain plants and animals give off the heartless light.
(D) is the heartless light given off by certain plants and animals.

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統計： A(2), B(0), C(1), D(0), E(0) #3848045