Read the following passage and fill in the blanks with the given words. 阅读下列文章,在空白处填上合适词汇的选项。
A.
quiet
B.
open
C.
take
D.
obey
E.
allowed The reading room is 46 between 8:30 a.m. and 6:00 p.m from Monday to Friday.I hope everyone can 47 the rules. 1.After you enter the reading room, you should keep 48 . 2. You are not 49 to read or speak aloud . 3. You can ’ t have snacks. 4. You are not allowed to smoke. 5. You are not allowed to 50 the books out of the reading room.
【简答题】如图 1-28 所示电路中,已知 E 1 =12 V , E 2 =4 V , R 1 = R 2 =1 Ω , R 3 =4 Ω , R 4 =7 Ω 。求: ( 1 )当开关 S 断开时,流过电阻 R 4 的电流 I 及其电压 U ; ( 2 )当开关 S 闭合后,用叠加原理求解流过 R 4 的电流 I 。