在如图所示的电路中，R1、R2为定值电阻，R3为可变电阻，电源的电_爱下问搜题

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问题选择题

在如图所示的电路中，R₁、R₂为定值电阻，R₃为可变电阻，电源的电动势为E，内阻为r．设电流表A的读数为I，电压表V的读数为U．当R₃滑动触点向图中a端移动，则（　　）

A．I变大，U变小

B．I变大，U变大

C．I变小，U变大

D．I变小，U变小

答案

当R₃的滑动触点向图中a端移动时，R₃变小，外电路总电阻变小，则由闭合电路欧姆定律知，总电流I变大，路端电压变小，则有U变小．电路中并联部分电压变小，则I变小．

故选D

补全对话，情景问答

Complete the dialogue with proper words or sentences.

A: Good morning, madam!

B: Good morning, sir!

A: You look worried. 1._____________?

B: My son got lost when I was talking with my friend in the park. I've looked

for him everywhere, but I can't find him. What shall I do?

A: 2._____________. Tell us something about him, and we can help you.

B: Thank you, sir.

A: Now please tell me 3._____________.

B: He's six years old.

A: 4._____________?

B: He's thin and tall with big eyes.

A: What is he wearing today?

B: He's wearing a white T-shirt and blue jeans.

A: 5._____________?

B: It's 13803677057.

A: OK. We'll call you as soon as we find him.

B: Thank you very much.

填空题

在深度为5的完全二叉树中，度为2的结点数最多为【1】。