图1—1所示c为（）的焊缝形式。
A.平焊缝
B.V形焊缝
C.X形焊缝
D.立焊缝
参考答案：C
There’s another way to survive this competition -- a way no one ever seems to tell you about, _____ you have to learn for yourself.
A．one
B．it
C．that
D．another
腹足纲的结构特点是什么？
