问题描述：
情态动词：She must have gone back to the vally.
－She must have gone back to the vally.
－No,she ___ the entrance to iy was no where to be found.
A mustn't B couldn't C hadn't
为什么
－She must have gone back to the vally.
－No,she ___ the entrance to iy was no where to be found.
A mustn't B couldn't C hadn't
为什么
问题解答：
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