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下面哪一個題目對三年級學生最為困難? (A)一條彩帶 4 公分,5 條彩帶合起來共長幾公分? (B)小雄有 4 件襯衫,5 條長褲, 小雄 可以搭配出幾套外出服? (C)媽 媽 買 了 4 打 鉛 筆 , 每 打 12 枝 , 請 問 媽 媽 一 共 買 了 多 少 枝 鉛 筆 ? (D)小方用白色積木排出一個 4 列,6 排的陣列,請問小方用了多少個白色積木?

28. Albert:_____________________Elissa:Oh, I see. I’ll add you later.(A) See you tomorrow. (B) Merry Christmas!(C) I just sent a friend request to you on Facebook. (D) I am full.

29. Anne:When will the football game start?Bill:In five minutes. ___________ We’re late.(A) Hurry up! (B) Time to go home.(C) Where? (D) It rains in summer.

30. Mark:Hi, Tony. What do you do to keep fit? Tony:____________________ Do you want to go with me? Mark:It sounds like a great idea!(A) It’s not your fault. (B) You are the painters.(C) I’m sure. (D) I swim seven times a week.

18. The RC circuit shown in the figure $(\mathrm{R} = 100\Omega, \mathrm{C} = 10\mu \mathrm{F})$ is called a low-pass filter because it passes low-frequency AC signals with less attenuation than high-frequency signals. The frequency at which the voltage ratio $\mathrm{A} = \mathrm{v_{out}} / \mathrm{v_{in}}$ drops to $1 / \sqrt{2}$ of its maximum value is known as cutoff frequency. What is the cutoff frequency of this circuit?(A) $159.2\mathrm{Hz}$(B) $1\mathrm{kHz}$(C) $6.28\mathrm{kHz}$(D) $1.59\mathrm{MHz}$(E) $10\mathrm{MHz}$

19. A radio-wave transmitter and a receiver are separated by a horizontal distance $d = 60.0 \, \text{m}$. Both antennas are located at a height $h = 40.0 \, \text{m}$ above the ground, as shown in the figure. The receiver detects two signals: one travels directly from the transmitter, and the other is reflected from the ground. Assume the ground is perfectly level and that a $180^{\circ}$ phase shift occurs upon reflection. What is the longest wavelength that results in destructive interference at the receiver?(A) $20.0\mathrm{m}$ (B) $26.7\mathrm{m}$ (C) $40\mathrm{m}$ (D) $80\mathrm{m}$ (E) $160\mathrm{m}$