—Mom，dad is smoking again!—Well，let him cut it ________ gradually since old habits die hard.

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

We can get a lot of useful information on the Internet; ______, the Internet also provides us with a new way of communication.

His report was so exciting that it was   __   interrupted by applause（掌声）.

 The problem is not ____ so easy as you think. It’s far from being settled.