A:How
B:What
C:Which
D:Where
The two girls _____ how to dance one month ago and now they can dance well.
明史专家吴晗在《朱元璋》一书中曾这样描述我国古代的君臣关系:“在宋以前有三公坐而论道的说法;到宋朝便不然了。从太祖以后,大臣上朝在皇帝面前无坐处,一坐群站;到了明代,不但不许坐,站着都不行,得跪着说话了”。君臣关系从坐而站而跪,说明中国古代中央政治制度演变的重要特点是( )