问题 单项选择题

甲、乙、丙三人沿着400米环形跑道进行800米跑比赛,当甲跑1圈时,乙比甲多跑1/7圈,丙比甲少跑1/7圈。如果他们各自跑步的速度始终不变,那么,当乙到达终点时,甲在丙前面:()。

A.85米

B.90米

C.100米

D.105米

答案

参考答案:C

解析:

当甲跑一圈时,乙比甲多跑1/7圈,丙比甲少跑1/7圈,由此可知乙、甲、丙的速度比为8/7:7/7:7/6,即为8:7:6。根据路程公式,在时间相等的情况下,路程比等于速度比,所以当乙跑800米时,甲跑700米,丙跑600米。所以,甲在丙前100米。

单项选择题

Lying in the sun on a rock, the cougar(美洲狮) saw Jeb and his son, Tom, before they saw it. Jeb put his bag down quickly and pulled his jacket open with both hands, making himself look big to the cougar. It worked. The cougar hesitated, ready to attack Jeb, but ready to forget the whole thing, too.

Jeb took off his jacket, grasped Tom and held him across his body, making a cross. Now the cougar’ s enemy looked even bigger, and it rose up, ready to move away, but unfortunately Tom got scared and struggled free of Jeb.

"Tom, No !" shouted his father.

But Tom broke and ran and that’ s the last thing you do with a cougar. The second Tom broke free, Jeb threw himself on the cougar, just as it jumped from the rock. They hit each other in mid-air and both fell. The cougar was on Jeb in a flash, forgetting about Tom, which was what Jeb wanted. Cougars are not as big as most people think and a determined man stands a chance, even with just his fists. As the cougar’s claws got into his left shoulder, Jeb swung his fist at its eyes and hit hard. The animal howled(吼叫)and put its head back. Jeb followed up with his other fist. Then out of the comer of his eye, Jeb saw Tom. The boy was running back to help his father.

"Knife, Tom," shouted Jeb.

The boy ran to his father’ s bag, while Jeb started shouting as well as hitting, to keep the cou-gar’s attention away from Tom. Tom got the knife and ran over to Jeb. The cougar was moving its head in and out, trying to find a way through the wall. Jeb was making out of his arms. Tom swung with the knife, into the cougar’ s back. It howled horribly and ran off into the mountains.

What do we know about cougars()

A. They are afraid of noises.

B. They hesitate before they hit.

C. They are bigger than we think.

D. They like to attack running people.

单项选择题