Correct the errors in the follow

Correct the errors in the following sentence.
Because he had eaten and drunk too much. He had to leave the party early. His stomach was like a volcano. That was ready to erupt.
【正确答案】：Because he had eaten and drunk too much, he had to leave the party early. His stomach was like a volcano (which) that was ready to erupt.
【题目解析】：p41