--- Don't worry. I've just sent an ambulance to you. They be there any second.
A. could
B. might
C. would
D. should
网友回答
A. could
B. might
C. would
(答案→)D. should
解析：考察情态动词辨析。A可能，也许；B也许；C会，过去常常；D应该；句意：不要担心，我已经排了一辆救护车了，他们应该很快就到了。根据句意说明should表示推测，意为：应该。是一个留有余地的推测。故D正确。