He spent every Sunday evening the piano in an old people's home.
A:to play
B:playing
C:play
D:plays
如果等差数列{an}中,a3+a4+a5=12,那么a1+a2+⋯+a7= ( )
鸟卵的结构如图所示,其中发育成雏鸟的结构是( )