问题
选择题
31. All books ______ to the library more than three days late will be subject to a fine.
A．return
B．returning
C．to return
D．Returned
答案
答案：D
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31. All books ______ to the library more than three days late will be subject to a fine.
A．return
B．returning
C．to return
D．Returned
答案：D