下列各组单词划线部分的字母组合哪一组发音不同。
I can’t swim. And she can’t, _______.
I was doing my homework _______ a dog came in.
—Marycan’thelp___thehouse.Why?—Becausesheisbusy____ahotelreservation.
It is about _______by bus from here to Harbin.
It’s impossible for us ____ there on foot in two hours.