图是人的膝跳反射示意图.据图回答:
生物体内含Zn2+的酶最多,有七十多种酶的活性与Zn2+有关,缺乏Zn2+的生物就无法正常生活,这说明无机盐( )
She couldn't ____ ( see/saw),when she was two years old.