---I saw Betty       to Grandpa Li's home just now.---Yes. She’s often seen _________ the old man with the housework.

Many sheep _______ eating grass by the river.

---________shall we deal with the waste paper. bottles and boxes?---Let’s keep them for recycling. It’s good for the environment.

The number of people invited to the party ____ fifty, but a number of them ____ absent for different reasons.

Over 20% of the students at that school _____ the habit of smoking, which is beyond imagination.