By the time Einstein was 14 years old, he ________ himself advanced mathematics.

       A. has taught                                     B. taught

C. had taught                                     D. was teaching

By the time Einstein was 14 years old, he ________ himself advanced mathematics.
 A. has taught      B. taught 
C. had taught      D. was teaching

By the time Einstein was 14 years old, he_______ himself advanced mathematics.

A. has taught　 B. taught

C. had taught　　 D. was teaching

完形填空：

阅读下面短文，掌握其大意,然后从1～15各题所给的四个选项中，选出一个最佳答案．

　Albert Enistein was from 　1　Jewish family． He 　2 　in Germany．　　 When he was a boy, he liked 　3 　questions．　　 By the time he was fourteen years old, he 　4 　advanced mathematics all by himself． 　5 　then he had decided to become a　　 　6 　and devote himself to abstract research．

　His family was not 　7 　, but his parents managed to send him 　8 　a technical school and 　9 　to the Federal Institute of Technology in Switzerland． After graduation, he 　10 　to　　 teach． Later he worked in a government 　11　　 　． Then with the money he saved, he continued his studies at　　 　12 　University of Zurich． In 1905 he got a 　13 　degree．　　 It was at that time 　14 　he began the research and studies　　 　5 　led to his famous theory of　　 Relativity．