The middle-aged scientist who( )abroad for 20 years by the end of next month,is on the way back to
问题描述：
The middle-aged scientist who( )abroad for 20 years by the end of next month,is on the way back to
his moterland.
A.had been B.is staying C.will have been D.will stay
答
C,by the end of next month是典型的完成式标志,但是next month 表示将来,因此应该用将来完成式,即will have been~