He _______ an English club last year and has improved his English a lot.
A:protected
B:produced
C:joined
D:received
下列各句中,没有语病的一句是( )
已知从n边形的一个顶点出发共有4条对角线,其周长为56,且各边长是连续的自然数,求这个多边形的各边长.