一质点绕半径为R的圆匀速运动了半周，所用时间为t．在此过程中该质点的（   ）

一个长方体的三视图如图，若其俯视图为正方形，则这个长方体的表面积为（　　）

A

    Tom is an eight-year-old student in Grade three. He is not interested in his lessons. He spends most of his time playing basketball. At night, he doesn't sleep until very late in order to play. In the morning, he usually gets up late and hurries to school. Sometimes he sleeps in class.

    Tom's father is worried about his poor schoolwork. He tried to make him work harder. One day, his father said to him, "My boy, if you get one hundred marks in the exam,  I'll buy a new basketball for you." The boy was very happy to hear that.

    The next day  Tom came running home. "Oh, Dad, I got one hundred." He shouted, "I got forty in English this morning and sixty in Chinese this afternoon!"

根据短文内容判断正误。

①a= $\frac{1}{3}$ ，b= $\frac{1}{4}$ ，c= $\frac{1}{5}$ ②a=6，∠A=45°；③∠A=32°，∠B=58°；④a=7，b=24，c=25 ⑤a=2，b=2，c=4．