【题目】______ he was 12, Einstein had learned advanced mathematics by himself.
A. The first time B. At the time
C. By the time D. During the time
在线课程【答案】C
【解析】考查连词：A．The first time第一次做---的时候，B．At the time在…那个时候，C．By the time到…时候为止，D．During the time在那期间，四个选项BD不能做连词，A的意思不对，选C，句意：到他12岁为止，爱因斯坦已经自学了高等数学。选C。