________ the machine begins to work, you can’t stop it _____.

Although China has developed its economy greatly, its per capital GDP is still         one-tenth of the United States.

The charity sale our school organizes every year has taught us much. _______ we would never have learned it in class.

My computer is ________ in need of repair because it does not work at all.

With the word “ PM2.5” _________ appearing in media reports, people pay greater attention to it and seek health tips for smoggy days.