Mike always loves ships. When he was older, he said, “I'm going to be a soldier.” But his eyes were not very1and he did not get in.

    Then he said, “I'm going to2a small boat and I'm going around the world.” But boats were very expensive, and Mike did not have enough3

    Last summer Mike found a swimming4near his house. The lessons did not cost very5 and Mike began going to the school at every end of the week and having6. Now he is a good swimmer.

    Last week a little boy said to him, “You're a very good swimmer. How do7learn to swim so well?”

    “I'm not good at all,” Mike said and he smiled. “8 I'm in the water, I say to myself, “There are 9fishes behind me!” Then I'm very afraid, and I10quickly.”

吊车以2m/s的速度将重物1×10⁵N匀速向上提起，这时钢索对重物的拉力 ____ N；若钢索改为以3m/s的速度使重物匀速下降，此时钢索对重物的拉力大小是____N。

函数$f\left(x\right)=-\frac{x}{e^x}$ (a<b<1),则           （    ）