题干

关于运动的合成,下列说法中正确的是(   )

A:如果合运动是曲线运动,其分运动至少有一个是曲线运动

B:两个直线运动的合运动一定是直线运动

C:两个分运动的时间一定与合运动的时间相等

D:合运动的加速度一定比每一个分运动的加速度大

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C

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Living places

The home of the elephant is in the deep forest. It is the largest of all land animals, and is found both in Asia and Africa. One of the main places in Asia where the elephant lives is the island of Ceylon. The huge forests on the island become the home of thousands of elephants. The trees grow thick and tall. They make many parts almost dark, while bright sunlight is above and around them.

Living habits

The elephant likes the deep part and the coolest places of the forest. There he will stand swinging his ears, to drive away the flies; or he will pull down a branch (树枝) from a tree to fan himself. He likes bathing, and to be near a lake or running water. There he takes in the water with his trunk, and spreads it all over his body.

Food

The elephant enjoys the fruits in the forest, and also the leaves of the trees. There is plenty of food for him in the forests, though he is not always happy with what he finds there.

Way of movement

When a group of elephants moves about in the forest, the oldest goes first. The young elephants and their mothers are in the middle, where they are safest. Then all move along with a great noise, the branches of the trees bending and breaking before them. Though the elephant is usually harmless, no one dares to attack (袭击) a group of them moving through the forest.

How people treat them

In Asia the elephant is trained to work. At one time the African elephant also was trained. Soldiers in ancient times often went to fight on the backs of African elephants. But now the elephant that lives in Africa is illegally (非法地) hunted mainly for its valuable ivory. In order to protect them, governments around the world have developed laws to stop this.