请指出该英文句子的语法错误.

楼主好,
若Write a letter to make an apology and suggest a solution为祈使句,则无错误.
反之,
修改如下,
Writing a letter to make an apology and suggest a solution.
或者
Making an apology and suggesting a solution by writing a letter.
再问： 请问原句make和suggest不需要因为在介词to后而需要变成动名词形式吗？谢谢。
再答： 原句的to做的动词不定式 不是介词