在水平地面上平铺n块砖，每块砖的质量均为m，厚度均为h。若将砖一块一块地叠放起来，至少需要做功 。
n(n-1)mgh/2
No one expected house prices to fall, but _____ that's exactly what happened. [ ]
A. moreover
B. thus
C. anyway
D. however
矿热电炉按炉缸可分为：（）式电炉和（）式电炉。
