1.He was only in

1.He was only in ----at the time?
A.his 20's B.the 20's C.his twenties D.the twenties
2.------of the popuiation here are peasants.
A.20 percents B.the 20 percent C.20 percent

在某某年代（这十年里）：
in the 1980s
in one's XXs是固定词组,意思是在一个人多大的时候.
那个时候他才20多岁吗?
选A.
percent
百分之一[C]
Thirty percent of the farmland has been planted to oil crops.
百分之三十的农田已种上油料作物.
Over ninety percent of the islanders here are illiterate.
这儿的岛民,百分之九十以上都是文盲.
选C.