It is very important for us_____ English well.

By now, no one has _______ a convincing explanation of why dinosaurs died out, and it remains a mystery.

Shanghai is the first city in the world _____________ a high-speed maglev train，from the city to Pudong Airport．

Mom, I will eat less fast food this year, believe me.—If you make a ________, you must keep it.

He often dislikes your ideas, ________ he- ________ . We often have different thoughts.