问题 选择题
如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力的带电粒子从坐标原点O处以速度v进入磁场,粒子进人磁场时的速度方向垂直于磁场且与x轴正方向成120°角,若粒子穿过y轴正半轴后在磁场中到x轴的最大距离为a,则该粒子的比荷和所带电荷的正负是(  )

A.,正电荷

B.,正电荷

C.,负电荷

D.,负电荷

答案

答案:C

单项选择题 A1/A2型题
阅读理解

阅读理解

     Robert Todd Duncan was born in 1903 in the southern city of Danville, Kentucky.His mother was

his first music teacher.As a young man, he continued his music study in Indianapolis, Indiana.

     In 1930, he completed more musical education at Columbia University in New York City.Then he

moved to Washington.For fifteen years, he taught music at Howard University in Washington.At that

time, not many black musicians were known for writing or performing classical music.Teaching at

Howard gave Duncan the chance to share his knowledge of classical European music with a mainly

black student population.  He taught special ways to present the music.These special ways became

known as the Duncan Technique.

     Besides teaching, Duncan sang in several operas with performers who were all black.But it seemed

that he always would be known mainly as a concert artist.However, his life took a different turn in the

middle 1930s.At that time, the famous American music writer George Gershwin was looking for

someone to play a leading part in his new work Porgy and Bess.The music critic (评论家) of the New

York Times newspaper suggested Todd Duncan.Duncan had almost decided not to try for the part as

he knew it would not be easy to get it.But he changed his mind.He sang a piece from an Italian opera

for Gershwin.He had sung only a few minutes when Gershwin offered him the part.He became famous

because of the part in Porgy and Bess.

     Todd Duncan gained fame as an opera singer and concert artist.But his greatest love in music was

teaching.When he stopped teaching at Howard, he continued giving singing lessons in his Washington

home until the week before his death.

1. What is this passage mainly about?

A. What Robert Todd Duncan loved most.

B. How Robert Todd Duncan became famous.

C. Robert Todd Duncan and his works of music.

D. A brief introduction to Robert Todd Duncan.

2. According to Paragraph 2, while teaching at Howard University, Duncan________.

A. found special ways to present music

B. opened doors for other black classical singers

C. had the chance to know many famous black musicians

D. became known for writing and performing classical  music

3. What happened to Duncan in the middle 1930s?

A. He gave up teaching at Howard University.

B. He was introduced by the New York Times in detail.

C. He was asked to be in charge of the opera Porgy and Bess.

D. He was given a big opportunity to become an opera singer.

4. We can infer that Robert Todd Duncan didn't at first want  to try for the part mainly because_____.

A. he was too busy to do it

B. he was not interested in it

C. he was not confident enough

D. he didn't want to become famous

5. Based on the passage, what did Robert Todd Duncan love most?

A. Singing in concerts.  

B. Writing music.

C. Singing opera.  

D. Teaching music.