什么是线性系统？其最重要的特性是什么？

(Phone call)Daughter: OK, Dad. Nice talking to you and glad everything's all right. ______ Dad: All right. Good-bye. Daughter: Good-bye, Dad.

A．Say "How are you？" to Mom

B．Say "Are you OK "to Mom

C．Give Mom our care

D．Give Mom our love

(Phone call) Daughter: OK, Dad. Nice talking to you and glad everything's all right. ______. Dad: All right. Good-bye. Daughter: Good-bye, Dad.

A．Say "How are you？" to Mom

B．Say "Are you OK" to Mom

C．Give Mom our care

D．Give Mom our love

(Phone call)

Daughter: OK, Dad. Nice talking to you and glad everything's all right. ______.

Dad: All right. Good-bye.

Daughter: Good-bye, Dad.

A．Say "How are you？" to Morn

B．Say "Are you OK " to Morn

C．Give Morn our care

D．Give Mom our love

Dad: All right. Good-bye.Daughter: Good-bye, Dad.A.Say "How are you？" to MomB.Say "Are you OK" to MomC.Give Mom our careD.Give Mom our love

– Are you sure about this？ -- _______________.

A、Absolutely.

B、About what？

C、Nice talking with you.

D、See you next week.

What need to be put down when you are taking a message through the phone？

A.The reason of calling.

B.The time and date of the call.

C.What needs being done after the call.

D.Where the call is from.

'll be fine. I only want to make a phone call. Joan: Here you are.

A．Sorry, I've no money at hand now.

B．Why do you want it？

C．Are dimes and quarters OK？

D．What on earth do you want？

Bill; Excuse me.______

Tom; Let me see. Are dimes and quarters OK？

Bill; I want to make a long distance phone call.

Tom; Then you' 11 need small change.

A．Do you have any money？

B．May I borrow your telephone？

C．Do you have the time, please？

D．Could you give me some change？

What needs to be put down when you are taking a message through the phone？

A.The time and date of the call.

B.The reason of calling.

C.What needs being done after the call.

D.Where the call is from.