Triangle ABC has vertices at A(3 , 7), B(5, 7), and C(3, 1). Which statement proves that triangle ABC is a right triangle?

A) AC = BC
B) AB ⊥ BC
C) AB ⊥ AC
D) AC ⊥ BC

Why can't my rank go i have 1723 points, but my rank is only at ambitious, which is only 250 points! like, (p.s. i know this isn't related to math, but i just don't know why it's doing this and i would really appreciate if someone could tell me whats going on with this)