PN码对载波信号的调制属于哪种调制？（）
A.相位调制
B.频率调制
C.幅度调制
D.脉冲编码调制
参考答案：A
— You should apologize to her, Barry. — __________, but it’s not going to be easy.
A．I suppose so
B．I feel so
C．I prefer to
D．I like to
根据句意用括号内所给词的正确形式填空:
1. My parents often tell me to listen to the teacher_______ (careful).
2. Every year, many_______ (visit) come to China to climb the Great Wall.
3. My brother is old enough to take care of _______ (he).
4. What's your _______ (weigh), Kate? Oh, it's a secret.
5. People can't live _______ (with) air or water.
