Bob was happy. He was at a new school, and students there were friendly. "Hi, Bob!" some students greeted him, but some students said, "Hi, Peter!" Bob didn't understand. He asked one student. "Why do some students call me Peter?"
"Oh, that's easy to answer," the students said, "Peter was a student here last year. Now he is at a different school. You look like Peter. Some students thought that you were Peter."
Bob wanted to meet Peter. He got Peter's address from a student and went to Peter's house. Peter opened the door. Bob couldn't believe his eyes. He looked really like Peter! Bob and Peter had the same color eyes and same smile. They had the same black hair. They also had the same birthday. And they both were adopted(领养)by two different families.
Bob and Peter found out that they were twin brothers. Soon after the boys were born, one family adopted Bob, and another family adopted Peter. Bob's family never knew about Peter, and Peter's family never knew about Bob.
Soon Bob and Peter's story appeared(出现)in the newspaper. There was a photo of Bob and Peter next to the story. A young man called John saw the photo in the newspaper. John couldn't believe his eyes. He looked like Bob and Peter! He had the same color eyes and the same smile. He had the same black hair. He had the same birthday. And he, too, was adopted by another family.
Later John met Bob and Peter. When Bob and Peter saw John, they couldn't believe their eyes. John looked really like them! Why did John looked really like Bob and Peter? You can guess. Bob and Peter are not twins. Bob, Peter and John are triplets.
小题1:Bob felt_______ at the new school.
A．interested
B．happy
C．sad
D．sorry小题2:Some students in Bob's new school thought_______.
A．John was Peter
B．Bob was John
C．Bob was Peter
D．Peter was John小题3:John knew the story of Bob and Peter from_______.
A．a newspaper
B．a book
C．his classmates
D．his parents小题4:The underlined word "triplets" in last paragraph means"_______"．
A．挚友
B．双胞胎
C．三胞胎
D．表兄弟
的光滑圆弧轨道相切于C点，AC=7R，A、B、C、D均在同一竖直面内。质量为m的小物块P自C点由静止开始下滑，最低到达E点（未画出），随后P沿轨道被弹回，最高点到达F点，AF=4R，已知P与直轨道间的动摩擦因数
，重力加速度大小为g。（取
）
、竖直相距Ｒ，求Ｐ运动到Ｄ点时速度的大小和改变后Ｐ的质量。
