Lying in the sun on a rock, the cougar 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 just with 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 cougar’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.

Why did Jeb pull his jacket open when he saw the cougar

A．To get ready to fight.

B．To frighten it away.

C．To protect the boy.

D．To cool down.

柴油机气门弹簧长期在高速下工作，金属材料产生（）现象，导致弹簧弹性减弱或折断。

A.缩短

B.伸长

C.疲劳

D.失稳