_______we keep our hearts open, we can experience the happiness friendship brings us.
A:Since
B:If
C:Unless
D:Though
—I don't want to do as ____sports as Tony does.—But you have to do if you want to be as _____as he.
空气有一定的体积,也有一定的形状。( )
下列五代中的政权,废掉唐朝皇帝而建立的是( )
该图中是松花江、长江、黄河、珠江四条河流的观测数据,其对应关系正确的是( )