The pencil with which he wrote was broken
句意：他用来写字的笔坏了
因为在which引导的定语从句中 which指代The pencil,所以他是用笔写字的
为with 即he wrote with the pencil
he built a telescope with which he could study the skies
句意：他建造了一个用来研究天空的望远镜
因为在which引导的定语从句中 which指代a telescope ,同上句,with为使用……的意思,即he could study the skies with a telescope
The woman ,from whom i learned the news ,is a nurse
因为要表达 我从她这里听到消息的 意思
所以为from 即i learned the news from the woman