(SAT Prep) For the figure, which of the following is true? I. m∠1+m∠2=m∠6+m∠5
II. m∠1+m∠3=m∠6+m∠4
III. m∠1+m∠3+m∠6=m∠2+m∠4+m∠5

A. I only
B. I and II only
C. II only
D. II and III only