DMT调制技术的主要原理是将频带（0—1.104MHz）分割为（）个由频

搜题请搜索小程序“爱下问搜题”

问题单项选择题

DMT调制技术的主要原理是将频带（0—1.104MHz）分割为（）个由频率指示的正交子信道（每个子信道占有4kHz带宽），输入信号经过比特分配和缓存，被划分为比特块，再经TCM编码后进行512点离散傅利叶反变换（IDFT）将信号变换到时域，这时比特块将转换成256个QAM子字符。

A.254

B.255

C.256

D.257

答案

参考答案：C

选择题

已知0.02 mol/L^-1CH₃COOH溶液和0.01 mol /L^-1NaOH溶液以等体积混和后溶液呈酸性，则该混合液中微粒浓度关系正确的[ ]

A．c (CH₃COO^-)＞c (Na⁺)

B．c (Na⁺) + c (H⁺) =c (OH^-) +c (CH₃COOH)+c (CH₃COO^-)

C．c (CH₃COOH)＞c (CH₃COO^-)

D．c (CH₃COOH)+c (CH₃COO^-)=0.02 mol/L-1

填空题

时态填空。

1. There (be) a parents' meeting next week, isn't there?

2. We look forward to (hear) from you soon.

3. My sister (not stay) at home last Sunday.

4. I asked him (not make) a noise because my mother was sleeping.

5. We were tired after a long walk, so we stopped (have) a rest.

6. You should (say) sorry to her. You made her (cry).

7. Be quick. Someone (wait) for you at the gate.

8. I heard the boy (sing) when I came back.

9. My daughter practises (play) the piano for two hours every day.