既是我国第一、二阶梯的分界线，也是东西走向的山脉是（　　）

人的眼睛像一架神奇的照相机，晶状体相当于凸透镜，视网膜相当于胶片，通过晶状体的调节将远近不同的物体成像在视网膜上。如图所示是不同位置处的两个物体的成像示意图，由图得出：眼睛看近处的物体时，晶状体的焦距____(选填“变大”、“变小”或“不变”)。人眼若长期观察近处物体，会造成晶状体过度弯曲，当他看远处物体时，像会成在视网膜的前方，应戴____透镜制成的眼镜加以矫正。

    Most elephants are grey. Only a few are white. It's difficult to see a white elephant. When people find a white elephant, they feel excited.

    Long ago, a white elephant was taken to the king. Only the king could have a white elephant. And the white elephant must be a very good one. People wanted to take a look at the animal. On its way to the king, the white elephant attracted(吸引) many people. They ran into the street and shouted, “A white elephant is coming!”

    All the people liked the cute elephant. Some gave it water to drink. Others sang songs to the elephant. A boy put a red hat on the elephant's head.

    Then the elephant came to the king. At last the king saw the white elephant. The king gave it a name himself. The elephant ate from gold dishes and it began a new life.