Using extraposition:To write her a letter to introduce yourself

Using extraposition:
To write her a letter to introduce yourself may be a good idea.
【正确答案】：It may be a good idea to write her a letter to introduce yourself.
【题目解析】：It做形式主语，真正的主语在句末，后移的结果就是满足了尾末重心的原则，达到强调的效果。