一中子与一质量数为A （A＞1）的原子核发生弹性正碰．若碰前原子核静止，则碰撞前与碰撞后中子的速率之比为（   ）

阅读下面短文，在空白处填入一个适当的词，或填入括号中所给单词的正确形式。

    Laura and Susie were born on the same day in the same hospital and at the same time. They{#blank#}1{#/blank#} (be) very close friends since they were very little. One bright sunny day, as I{#blank#}2{#/blank#} (walk) home from the shops, I decided to take a short cut {#blank#}3{#/blank#}the park. All of a sudden I heard a loud scream. It sounded like a child. With fright I dropped my shopping bag and ran in the {#blank#}4{#/blank#} (direct) of the noise.

    As I was getting {#blank#}5{#/blank#}(close) to the noise I saw two little girls, one of {#blank#}6{#/blank#} was screaming in pain. The other child was frozen to the spot with a look of terror on her face. As I ran towards them, I quickly realized that I knew the children. One was my daughter Laura and the {#blank#}7{#/blank#}was her best friend Susie.

    I was totally shocked to see the girls there, as they knew they were not allowed to go to the park alone. Obviously the girls {#blank#}8{#/blank#}(hear) strange noises and then decided to run as fast as they could to get away. While {#blank#}9{#/blank#}(run), Susie fell over and could not get up.

    Susie's mother and I had another talk with the girls about not wandering off without an adult then. Both of them learnt a {#blank#}10{#/blank#}(value) lesson.

阅读下面短文, 从短文后各题所给的四个选项(A、B、C、D)中, 选出可以填入空白处的最佳选项。

    William Franklin came to my class half a year ago.But from his first day here,he 1 himself in his own world and he never spoke to others.As his teacher,I tried to start a talk with him but 2.It seemed as if he just didn't want to break his 3.

    After the Thanksgiving holiday,we received the news of the4Christmas collection of money for the 5 in our school."Christmas is a season of 6,"I told my students."Some poor students in our school might not have a 7 holiday.By giving a little money,you will help 8 some toys,food and clothing for these needy students.We will 9 the collection tomorrow." 

    The next morning, 10 ,I found out almost everyone had 11 this matter except Willard Franklin.He came up to my desk with his head down. 12 ,he dropped two coins into the small box."I don't need milk for lunch,"he said in a 13 voice.

    After school I couldn't help sharing what had 14 in the morning with our headmaster."I may be wrong,but I 15 Willard might be ready to become part of our class. "I am 16 to hear that," he nodded."And I just received a list of the poor families in our school who most need 17 .Here,take a look at it."

    As I sat down to 18 ,I found Willard Franklin was at the top of the list.At that moment,I felt I really 19 Willard for the first time:a cold face with a warm heart.From this 20 ,I also learnt that whether rich or poor,every child has a kind heart.