一物体放在凸透镜前从很远处匀速靠近凸透镜，至透镜焦点处，考察像运动的速度，应该是（ ）
A．始终与物体的运动速度相同
B．先小于物体运动的速度，后来又大于物体运动的速度
C．先大于物体运动的速度，后来又小于物体运动的速度
D．始终大于物体运动的速度
物体从远处到二倍焦距这个过程中，由于此时所成的像是倒立的缩小的像，所以在相同时间内像通过的路程要小于物体通过的路程．故此时像的速度小于物体的速度．
到达二倍焦距之一瞬间，两者速度相等，因为此时的像与物等大．
从二倍焦距到一倍焦距的过程中，此时的像是放大的，所以在相同时间内像通过的路程要大于物体通过的路程．故此时像的速度大于物体的速度．
综上分析，故选B．
| Read and choose the correct answer. 阅读短文，选择正确的答案。 |
| Mr. Li is our English teacher. His home is near our school. Sometimes we go to his home. He has two sons. They are only five years old. They look like their father. They often wear the same clothes. We love to see them and play with them. Mr. Li calls them Da Bao and Xiao Bao. |
| 1. Mr. Li is the father of . |
[ ] |
| A. the two girls B. the twins C. us and the two boys |
| 2. Mr. Li's home is . |
[ ] |
| A. in the school B. near our school C. far away from the school |
| 3. The twins are years old. |
[ ] |
| A. ten B. four C. five |
| 4. The twins often wear . |
[ ] |
| A. the same clothes B. the blue shirts C. the same shirts |
| 5. The twins often play with . |
[ ] |
| A. their students B. their sister C. Mr. Li's students |