To prevent the air ___ ,something will have to ___.

ought you ______ for vacation tomorrow.   —I had planned to, but I have a very important meeting to attend tomorrow.

People from every corner of the world___China on the successful launch of Shenzhou VII.

The Boston Marathon bombings killed 3 people ， including a Chinese citizenShenyang

The question is quite difficult, so _______ students can work it out.