将下列句子改写成含有定语从句的句子.
问题描述：
将下列句子改写成含有定语从句的句子.
There were some people rowing on the river.
We are reading the letter written by Sara.
答
There were some people rowing on the river.There were some people who were rowing on the river.We are reading the letter written by Sara.We are reading the letter which was written by Sara.