把弯曲的公路改直可缩短里程，这根据的数学原理是( )
两点之间，线段最短
支机器时，用角度尺检查（）。
A、横臂水平度
B、大杆的垂直度
C、钻杆的垂直度
What troubles her is that she can't buy _____ she wants with the money she earns. [ ]
A. whatever
B. whichever
C. however
D. whenever
