方位介词 — 英语词汇题

看中文提示，写出句中所缺的方位介词。1. The pencil is u______ the desk.（在……下面）2. My schoolbag is o______ the chair.（在……上面）3. The ball is b______ the door.（在……后面）4. The big tree is b______ the library and the playground.（在……中间）5. My ruler is i______ the pencil case.（在……里面）