若要求查找‘李’姓学生的学生号和姓名，正确的SQL语句是

A．SELECT S#,SNAME FROM S WHERE SNAME='李%'

B．SELECT S#,SNAME FROM S WHERE SNAME LIKE '李%'

C．SELECT S#,SNAME FROM S WHERE SNAME='%李％'

D．SELECT S#,SNAME FROM S WHERE SNAME LIKE '％李％'

何谓视觉的三原色学说？简述视锥细胞的色觉功能。