英语定语从句额、怎样把两句话连成一句呢?例如 Tom's our friend.He is running.希望给出答案

Tom, who is running, is our friend.
在把两句话连成一句话前,应先注意两句话中相同的人或事物,也就是寻找能把两句话联系起来的桥梁.如,上面两句话,he就是指Tom,指一个人,我们可以借助这一点联系前后两部分.who引导非限制性定语从句,指代先行词Tom,同时做is running的主语.
又如：The man is my brother.He is standing under the big tree.
The man who is standing under the big tree is my brother.