Will you lend me a pen to write with,为什么要用with?

Will you lend me a pen to write with,为什么要用with? Could you lend me a pen to write with?为什么要加with 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? I want to borrow a pen ____ to write with 为什么要用with Somebody,lend me a pen,will you? can you write this letter for me with a pen? I use a pen to write.还是I use a pen to write with.为什么? Do you have a pen to write with? please pass me a pen ___.A.to write on B.write with C.to wri write with a pen The pen is good to write为什么要加with Tom,please lend me a pencil(to draw a picture with).为什么这么用?w