Plastic bags are provided for our convenience but they have also_______ the pollution of the environment．

Start out right away, _____ you’ll miss the first train[ ]

His father, who is said to be teaching in Australia, ____ in Nanjing University for more than 10 years

Another cup of tea— No, thanks. I _______ be off. My mom is waiting for me at home .

It was on a cold winter evening_______ his father left home and was never back.