You read a book in the sun—it'll do harm to your eyesA. couldn'tB. wouldn'tC. needn'tD.

问题补充：

You read a book in the sun—itll do harm to your eyes．

A. couldn

B. wouldn

C. needn

D. mustn

答案：

A. couldn

B. wouldn

C. needn

(答案→)D. mustn

解析：其他动词辨析。A不可能；B不会；C不需要；D千万不能，禁止；结合句意可知D正确。句意：你千万不能再阳光下看书。它对你眼睛有很大的伤害。