单项选择题

A.-b+Sqr(b*b-4*a*c)/2*a
B.-b+Sqr(b*b-4*a*c)/(2*a)
C.(-b+Sqr(b*b-4*a*c))/(2*a)
D.(-b+Sqr(b*b-4*a*c))/2*a