Beforeyouhandinyourtestpaper……时间状语从句.
Before(连接词)you(主语)hand(谓语)in(状语)your(定语)test(定语)paper(宾语)……
Beforeyouhandinyourtestpaper……后面再加主句.如:Beforeyouhandinyourtestpaper,pleasetellme(主句).
动词和副词构成的短语叫动副短语,如:goacross.
动词和介词构成的短语叫动介短语,如lookat.
注意!在这俩个短语中使用代词时往往:动副短语可拆而动介短语不可拆.