China's population is about （ ） of the world's population.
（A）the quarter
（B）one - four
（C）a quarter
（D）one - fourths
He has toured all over China in his （ ）.
（A）thirtieth
（B）thirty
（C）thirty's
（D）thirties
In （ ） Marx began to learn Russian.
（A）the 1870s
（B）1870's
（C）1870s
（D）his 1870's
