如图所示实验装置,甲重16N,乙重12N,静止时不计弹簧测力计自重,则弹簧测力计的示数是( )
A:16 N
B:12 N
C:28 N
D:4 N
视觉的形成:光线依次经过____、____、 玻璃体、____、视觉神经、____七个阶段.
Peter is ten years old. He is _______ to go to school.