The boy was sitting under an apple tree _______ an apple fell onto his head.
A：when
B：while
C：after
D：before
下列关于青春期心理矛盾的叙述中，错误的是（ ）
What's the time ______ the clock?（ ）
六大板块中，几乎全部位于海洋的板块是（ ）
