Many scientists believe sea levels by more than one meter by the end of the 21st century.

问题补充：

Many scientists believe sea levels by more than one meter by the end of the 21st century.

A. will be risen

B. will have risen

C. will have been

D. will be rising

答案：

A. will be risen

(答案→)B. will have risen

C. will have been

D. will be rising

解析：考查时态：句意：很多科学家相信，海平面到21世纪末为止将会上升超过一米。时间状语是by the end of the 21st century.如果by+将来时间，谓语的时态应该是将来完成式，选B。