Which function has a removable discontinuity at x=7?

A) f(x)=3/x−7
B) f(x)=x²−10x+21​/x−7
C) f(x)={−x, x<7
{x+1,​ x≥7​
D) f(x)={x​/−x−7,​ x<7
{x+1, x≥7​