Given a∥b , and c is not parallel to a or b, which statements must be true?
m∠4=m∠5
m∠7=m∠11
m∠1=m∠5
m∠5=m∠12
m∠4=m∠5
m∠7=m∠11
m∠1=m∠5
m∠5=m∠12