People along the river didn’t allow them to ______ a factory so as not to pollute the water.

 Mary sings English songs well and ______.

It’s too late to go out now and        , it’s starting to rain.

Some physics problems in this book are _________difficult for the students _________work out.

—I am trying my best to learn English, but it doesn’t work well!—Don’t worry! Regard it _____ a big challenge!