Lei Feng always _____ others first.

Hi, Jack. Did you go to Lucy’s birthday party? —No, I felt so sad. I_______then.

Shanghai is bigger than_____ in Jiangsu and bigger than_______in China.

If _____ carefully, the experiment will be successful.

Jack, could you help me ________ these pictures on the blackboard? It may help us know more about the hazy weather. (雾霾) — With pleasure.