The girl 主 handed 谓 everything 宾(先行词)
( )she had picked up in the street to the police.定从 修饰先行词
在从句中picked up 后缺个宾语 就是前面那个 everything
所以 填个关系代词代替先行词到后面充当成分
因为是everything 所以只可以用 that 不可以用which
C 这里缺宾语
that跟which都可以做宾语
但是由于修饰的是不定代词everything,所以只能用that
主句:The girl handed everything to the police
定语从句:she had picked up in the street
从句中,she是主语,had picked up,pick up在这里相当于及物动词,后面要接宾语