30 % of the young trees attacked by diseases pine trees.A. isB. areC. wasD. has been

问题补充：

30 % of the young trees, attacked by diseases, pine trees.

A. is

B. are

C. was

D. has been

答案：

A. is

(答案→)B. are

C. was

D. has been

解析：本题考查主谓一致，百分数+名词，其后的谓语动词与名词保持一致，故谓语动词用复数。句意：遭受病害3 0%的小树是松树。