问题补充：
At the present time, more singing stars to be difficult to work with.
A. say
B. have said
C. are said
D. were said
答案：
A. say
B. have said
(答案→)C. are said
D. were said
解析：句意：目前，据说很多唱歌的明星很难共事。Be said to是固定用法，意思是据说，且根据时间状语At the present time，故用一般现在时，选C。
