A:四季的变化
B:昼夜长短变化
C:昼夜更替现象
D:昼夜现象
—I am really struck by your spoken English. You speak so fluently. Have you been abroad?
—Yes. I ______ in London for two years.
下列图像中x轴表示个别劳动生产率,y轴表示单位商品价值,其中正确反映两者关系的是( )。
计算:(﹣1)2011+2tan60°+20﹣27+|1﹣3|.