改错题。1. How old are your brother? He is t_爱下问搜题

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问题改错题

改错题。

1. How old are your brother? He is twelve. A B C	( )______
2. Are we classmate? Yes, we are. A B C	( )______
3. Are you friends? Yes, we're. A B C	( )______
4. Who is he? He's my cousin andy. A B C	( )______
5. They are fine friends. A B C	( )______
6. Amy is a girl. He's twelve. A B C	( )______
7. Who's your uncle? He's a doctor. A B C	( )______
8. Lucy and Lily are girl. They are eleven. A B C	( )______
9. Are you a teacher? Yes, I'm. A B C	( )______
10. He is tall. He is America. A B C	( )______

答案

1. B is 2. B classmates 3. C we are 4. C Andy 5. B good 6. B She's

7. A What's 8. B girls 9. C I am 10. C an American/ American

选择题

如果ax（3x-4x²y+by²）=6x²-8x³y+6xy²成立，则a、b的值为[ ]

A.a=3，b=2

B.a=2，b=3

C.a=-3，b=2

D.a=-2，b=3

计算题

（16分）空间有一竖直向下的匀强磁场，磁感应强度B＝0.8T，两相同的长方形金属板MN、PQ竖直平行放置，俯视如图。两板间距L＝0.20m，与两板间距等长的金属棒AB垂直放在金属板上，可无摩擦滑动，其电阻R₀＝4Ω，金属板的右边接有如图电路，电阻R₁＝4Ω，R_,2＝2Ω。现有不计重力的带电粒子以v₀=2m/s的水平初速度射入两板间，问：

（1）欲使粒子能保持水平方向做匀速直线运动，金属棒AB运动速度的大小和方向；

（2）若金属棒AB保持以（1）中速度做匀速滑动，作用在AB上的外力多大；

（3）若使金属棒在稳定运动过程中突然停止，则在停止运动的瞬间，作用在棒上的磁场力大小与方向。