问题
选择题
The boy the first prize, but he was so careless as to make a foolish mistake.
A．must have gained
B．need have gained
C．could have gained
D．shall have gained
答案
答案：C
考查情态动词。must have done 对过去事情肯定的推测，一定，need have done 本需要做某事，而实际上没有做，could have done 本可以做某事，而实际上没有做，句意：这个男孩本可以获得第一名的，但是实际上没有做。故选C。