--David has been away for more than 25 daysI miss him very much．You know 25 days short

问题补充：

--David has been away for more than 25 days．

--I miss him very much．You know，25 days short．

A. is

B. isn’t

C. are

D. aren’t

答案：

A. is

(答案→)B. isn’t

C. are

D. aren’t

解析：句意：大卫已经离开超过25天了。我很想念他，你知道。25天不短。25 days视为一个整体时为单数，系动词用is,根据语境可知25天很长，故选B.