题目

Jeff has a pet. It's a dog. It is white. Jeff likes it very much. He thinks the dog is very smart. It can play ball games and it can buy newspapers for Jeff. Every morning，Jeff puts one dollar into the dog's mouth and it goes to the shop to buy newspapers for Jeff. Jeff has a good friend Mark. Jeff tells Mark about his smart dog. Mark doesn't believe it. Today，Mark comes to see Jeff in the morning. Jeff is playing with his dog. Mark says，“I will give your dog money. I don't think it can buy newspapers.” “Have a try(试一下)．” says Jeff. Then Mark puts money into the do如右图所示，船从A处开出后沿直线AB到达对岸，若AB与河岸成37°角，水流速度为4 m/s，则船从A点开出的最小速度为 　　 A．2 m/s　　　 　　　　B．2.4 m/s C．3 m/s             D．3.5 m/s