指示剂发生颜色变化的（）范围，叫做指示剂的（）范围。
参考答案：PH值；变色
The soldiers are afraid that they will soon ________ oil and food if they are still surrounded. [ ]
A. run out
B. run out of
C. run across
D. run away with
望远镜对光的步骤是（）。
A.物镜对光、目镜对光、消除视差
B.目镜对光、物镜对光、消除视差
C.目镜对光、消除视差、物镜对光
D.物镜对光、消除视差、目镜对光
