have的用法：
have作助动词：
主要变化形式：have，has，had
动名词/现在分词：having
1）have +过去分词，构成完成时态，例：
He has left for London.他已去了伦敦。
By the end of last month， they had finished half of their work.
上月末为止，他们已经完成工作的.一半。
2）have + been +现在分词，构成完成进行时（现在完成时），例：
I have been studying English for ten years.
我一直在学英语，已达十年之久。
3）have+been +过去分词，构成完成时态的被动语态，例：
English has been taught in China for many years.
中国教英语已经多年。
