一Professor Li, ______the student start at once or wait a while? 一At once.
The students expected there ________ more free time before the test.
They tried to prevent the damage ________ their cattle.
His father disappeared, ________ two children and never _______ from again.
Does the way you thought of ________ the water clean make any sense?
In order not to be disturbed, I spend three days _______ in my study.