正四面体ABCD(六条棱长都相等)的棱长为1，棱AB∥平面，则正四面体上的所有点在平面$\alpha$内的射影构成的图形面积的取值范围是（   ）

“可燃冰”作为新型能源，有着巨大的开发使用潜力，同等条件下，“可燃冰”完全燃烧放出的热量达到煤气的数十倍，说明“可燃冰”的 ____很大．若以10倍的关系粗略计算，100g“可燃冰”完全燃烧放出的热量为　 ____J，可以使　 ____kg的水从20℃加热至60℃（c_水=4.2×10³J/（kg•℃），q_煤气=4.2×l0⁷J/kg）．

The long trunk of an elephant is a wonderful example of skill. The neck of four-footed animals is usually long, to have them reach their food without difficulty, but the elephant has a short neck, to make him more easily support the weight of his huge head and heavy teeth.   His long trunk lets him get his food easily.

The trunk of an elephant is to him what the neck is to other animals. It is also a nose to him, for at the end of it there is a empty place like a cup, and in the bottom of the cup are two holes, and the animal smells and breathes through them. It is an arm and a hand too, so that it has been said that the elephant carries his nose in his hand, and it might also have been said that he breathes by his hand.

 At the end of the trunk, there is a strange part, about five inches long, which forms a finger. With this finger the animal can pick up the smallest piece of money from the ground, and he has been taught to make marks like letters with a pen.

The trunk of a full-grown elephant is about eight feet long. The elephant has such great strength that he can knock down a man with it.

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