The police still haven’t found the lost child, but they’re doing all they .
A. can
B. may
C. must
D. should
网友回答
(答案→)A. can
B. may
C. must
D. should
解析：考查情态动词。can表能力， may可能，可以， must必须，D. should应该， do all（that）one can意为：“竭尽全力”。句意为：“虽然警察仍未找到那个失踪的孩子，但他们正竭尽所能。”选A。