I am too tired. I _____ my homework all morning. A have been doing B did C do D have done
As we all know, ______ knowledge comes from _______ practice.
We should prevent pollution ________ happily.
The line is engaged. I can’t _____ now.
It had rained for several days. The clothes had _____ near the fire to dry.
This kind of paper was as soft and light as silk but ______ expensive.