根据乘方的意义可知：53=5×5×5，54=5×5×5×5，则53×54=（5×5×5）×（5×5×5×5）=57即53×54=57。想一想：

均匀平面波从空气垂直入射到理想介质面（εr=2.25，μr=1，σ=0），则电场反射系数为（ ）。 A: R=-1/5 B: R=-2/5 C: R=-3/5 D: R=-4/5

均匀平面波从空气垂直入射到理想介质面（εr=2.25，μr=1，σ=0），则电场反射系数和折射系数分别为（ ）。 A: R=-1/5，T=4/5 B: R=-3/5，T=2/5 C: R=-1/3，T=2/3 D: R=-2/3，T=1/3

假定有两个关系R与S，其内容分别为： R关系 S关系 A B C B C D 1 2 5 2 5 17 2 5 6 2 5 9 3 5 4 5 4 1 (πA,B(R))×(πC(S))的运算结果为 ______。 A．A B C 1 2 5 1 2 4 2 5 5 2 5 4 3 5 5 3 5 4 B．A B C D 1 2 5 17 1 2 5 9 3 5 4 1 C．A B C S.B S.C D 1 2 5 2 5 17 2 5 6 2 5 9 3 5 4 5 4 1 D．A B C 2 5 6

由集成运算放大电路组成的反相器，当输入电压为Ui=-5V时，Auf=（）V。 A: 5 B: -5 C: 1 D: -1

数学表达式5R2,对应的表达式是()。 A: 5*R2 B: 5(R*R) C: 5*RR D: R*R*5

下列程序的运行结果是（ ）。t = 0 while t < 5: print(t, " is less than 5") t = t + 1else: print(t, " is not less than 5") A: 0 is less than 51 is less than 52 is less than 53 is less than 54 is less than 55 is not less than 5 B: 1 is less than 52 is less than 53 is less than 54 is less than 55 is less than 55 is not less than 5 C: 0 is less than 51 is less than 52 is less than 53 is less than 54 is less than 5 D: 1 is less than 52 is less than 53 is less than 54 is less than 55 is less than 5

【单选题】下面程序执行结果() #include main() { int i ,j ; for(i=1; i<=5; i++) { for(j=1; j<=i; j++) printf("%2d",i); printf(" ",); } } A. 1 2 2 3 3 3 4 4 4 4 5 5 5 5 5 B. 1 2 3 4 5 C. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D. 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

我国民族自治地方的面积占全国总面积的（） A: 64、5% B: 54、5% C: 74、5%

如图所示电路，已知ε1=5 V，ε2=3 V，R内1=R内2=1 Ω，R1=R2=R3=2 Ω，则Uab=[img=218x121]17e0aaba219d507.jpg[/img] A: 5 V B: 2 V C: -1 V D: 1 V E: -2 V