在书上看到一句:Ron gave a slight cough, which might have been hiding a snigget.出自《哈利波特》,翻译是:罗恩轻轻咳了一声,免得笑出声来。我想知道,might have been doing是情态动词的什么形式呢?在书上只看到might have done,这里might have been doing是什么语法结构?有什么特殊的讲究吗?为何出现在这句话中?请指点啊,求分析和解答,不要重复翻译了,谢谢