①∠A=2∠BFC﹣180°;②DE﹣BD=CE;③△ADE的周长等于AB与AC的和;④BF>CF.
其中正确的有( )
A:①
B:①②
C:①②③
D:①②③④
关于力的概念,下列说法不正确的是( )
— I don't care what my teachers think.
— Well, you_______.