Using extraposition: That his invention will make people's life

Using extraposition: That his invention will make people's life more convenient is certain.
【正确答案】：It is certain that his invention will make people's life more convenient
【题目解析】：为了避免句子的头重脚轻，我们用形式主语it替代真正的主语“his invention will make people's life more convenient”。