问题
选择题
Edison was a clever boy, and ______ he was fourteen, he had learned advance mathematics by himself.
A．whenever
B．by the time
C．the moment
D．ever since
答案
Ｂ
考察时态。By the time到…时为止；根据he had learned advance mathematics by himself中的过去完成时，可知所选择的连词是与完成时连用的，结合句意可知Ｂ正确。句意：爱迪生是一个聪明的孩子。到他１４岁的时候，他已经自学了高等数学。