关于现在完成时否定式she hasn't forgoten the correct answer yet 为什么这里是用

关于现在完成时否定式she hasn't forgoten the correct answer yet 为什么这里是用 answer the single one correct 为什么这里correct 不用副词 She hasn't shut the window yet中的shut是原型吗 请问As might be expected,the plane hasn't arrived yet.里为什么要用mi When and where go for the holiday hasn't decided.为什么用现在完成时? The train hasn't arrived yet 为什么must的否定式要用can’t或者needn’t?may要用can’t 为什么must be的否定式是can't be而不是mustn't be 关于完成时改过去时Hasn't your friend arrived yet?现在完成时可不可以改成一般过去时Does grandma hasn't taken her medicine yet.Maybe she forgeot.(为什么 She hasn't returned the book to de library yet.等于什么? must的否定式是musn't还是mustn't