What will happen if the duplicate copy of the letter is not returned by the deadline？

This offer will be _____________ on that date.

On weekends, our landlady provided dinner in (add) _____ to breakfast.

The friendship conveyed in the gift seems to be the most (value) ____ thing.

Peace and development are the main themes of the times，an era full of both hope and challenges．

A)和平与发展是时代的主题，这个时代既充满希望，也充满着挑战。

B)和平与发展是时代的主题，这是个充满希望与挑战的时代。

C)多次讨论和平与发展这个主题，讨论充满了希望和挑战。

D)时代的主题是和平与发展，同时这个时代充满了希望和挑战。

根据以下材料回答51～55：

第51题办公钟地球仪

The (able) _____ that he showed in this field is really extraordinary.