黄土高原农业较发达、人口集中的地区是（　　）

已知三点P₁（x₁，y₁），P₂（x₂，y₂），P₃（1，-2）都在反比例函数y＝$\frac{k}{x}$的图象上，若x₁＜0，x₂＞0，则下列式子正确的是（　　）

    Tom always can't sleep well at night. But he was never late for work. He went to see his doctor on Sunday afternoon. He took the subway to get there. He met his boss on the subway and they talked for a while.

    Tom got some sleeping pills from the doctor. That night Tom took the pills. He had a nice sleep. He went to work happily on foot in the morning. Getting into the office, he said to his boss “I had a nice sleep and got up happily this morning.” “That's fine,” shouted the boss, “but where were you on Monday?”

如图，铁道口栏杆的短臂长（OA）为1.25m，长臂长（OB）为16.5m，当短臂端点下降0.85m时，长臂端点升高了____ m.（不计杆的宽度）