四级考试的语法提高练习

　　表示因果: for, so, therefore, hence 　　从属连词 　　表示时间: when, while, as, after, before, since, until, as soon as, once 　　表示原因: because, as, since, now that, seeing that 　　表示条件: if, unless, in case, provided, suppose, as long as, on condition , 　　表示其他关系: though, than, as 　　My father, who had been on a visit to America, returned yesterday. 　　All the books, which had pictures in them, were sent to the little girl.