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问题 单项选择题

某船以18kn航行1000nmile，需要燃油100t。现仅存燃油80t，但至目的港尚有800nmile的航程。船舶计划预留燃油20t作为备用，为了使船舶续航至目的港，试求该船应采用的航速（）。

A．15kn

B．15.6kn

C．16kn

D．16.5kn

答案

参考答案：B

解答题

已知O为坐标原点，曲线C上的任意一点P到点F（0，1）的距离与到直线l：y=-1的距离相等，过点F的直线交曲线C于A、B两点，且曲线C在A、B两点处的切线分别为l1、l2．

（1）求曲线C的方程；

（2）求证：直线l1、l2互相垂直；

（3）y轴上是否存在一点R，使得直线RF始终平分∠ARB？若存在，求出R点坐标；若不存在，说明理由．
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阅读理解

阅读短文，判断下列句子的正（T）、误（F）。

         I am in No. 10 Middle School. At School I have a good friend. He is an English boy. His name is Tom. He is twelve. We are not in the same class. He is Class 4, Grade 7. I am in Class 2. Tom's sister is not a student. Her name is Jane. She is five. She is a nice girl.

( )1. My friend Tom is from America.

( )2. We are not in the same class. He is in Class 2. I am in Class 4.

( )3. Tom has a sister.

( )4. Tom and his sister are students.

( )5. Tom and I are in No.10 Middle school.
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