It puzzles the scientists _____ some mammals produce their young _____ others lay eggs.
6. ---- You’ve finished off two pizzas!---- Yes. But the second is _______ little bit small, so may I have ______ third one?
5. Schools ban students from bringing mobile phones, which are used to _________ in exams.
4. I’m poor at English, so to make a speech in English at the meeting is ________ my ability.
3. We find _________ easy to get along with our new teachers here.
2. ---- English, as a living language, ________ all the time.---- Right. Who knows what it will be like in the years to come?