a chair to sit on;a pen to write with.这种怎么判断最后要不要加介词?

a chair to sit on;a pen to write with.这种怎么判断最后要不要加介词? I need a chair to sit on.I need a pen to write with. I found a chair to sit on Will you lend me a pen to write with?最后的介词问什么用with?语法点是什么? 请问：I want to have a chair to sit on∕in.on或in这种句末的介词一般在什么时候出现 please pass me a pen ___.A.to write on B.write with C.to wri There is a comfortable chair to sit on .为什么加on Could you lend me a pen to write with?为什么要加with 英语语法问题为什么句子"She find a chair to sit on."中"sit"后还要加"on",可以直接说 please pass me a pen ____ A to write on Bwrite with C to wri The pen is good to write(要加介词with吗?) i have a pen to write还是/write with