— I wonder ___ Mary has kept her figure after all these years.
— By working out every day.
A：where
B：how
C：why
D：If
下列关于俄罗斯地形和气候的叙述中正确的是（ ）
在▱ABCD中，过点D作DE⊥AB于点E，点F 在边CD上，DF=BE，连接AF，BF．
