【题目】 , when Marx was already , he found it was important to study the situation in Russia, so he began to learn Russian.
A.In 1870s, in his fiftiesB.In 1870s, in fifties
C.In the 1870s, in fifties D.In the 1870s, in his fifties
在线课程【答案】D
【解析】
考查时间表达和数词。句意：在十九世纪七十年代，马克思已经五十岁了，他觉得研究俄国的形势很重要，便开始学习俄语。in the 1870s十九世纪七十年代，年代前冠词必须是冠词the；in one's fifties在某人五十多岁时；表示在某人多大时，用 in one's+基数词的复数。故选D。