1.When Tom saw the accident happen,he called the polise____h

1.When Tom saw the accident happen,he called the polise____his mobile phone____once.
A.with on B.on at C.on with D.with at
2.The teacher spoke loudly_____the students could hear him clearly.
A.so B.that C.so that D.until
3.--You'll ralaxed when you return from your vacation.
A.You're right B.I hope so C.All right D. I hope not 请帮我解释一下