His father began to work____he was seventeen years old.A as old as B as early as B since D while

while (==when )是正确的选择.A as old as 的后面不能加句子B as early as的后面不能加句子B since 的主句必须是现在完成时D while (== when) 作为连接词,后面的句子谓语动词可以是be动词.又如：-------- He came un...