have to句型变换解析

have to do sth的句型表示主语“有必要或有义务做某事”。其中have的一般过去时用had,一般现在时第三人称单数用has。例: They had to go home on foot yesterday because the bus had gone. 昨天他们不得不走回家去,因为公共汽车已经开走了。 he has to look after her mother at home,for her mother is ill. 她不得不在家照看妈妈,因为妈妈病了。 在对have to句型进行疑问或否定变换时,若指通常或习惯上的动