I met Lucy in the primary school and we have been close friends _____.
A:as usual
B:again and again
C:sooner or later
D: ever since
解下列方程,最适合用公式法求解的是( )
证明:等腰三角形底边中点到两腰距离相等.(请画出图形并写出已知.求证及证明过程)