Answer:
Step-by-step explanation:
Given: ABCD is a parallelogram
To prove: ∠A and ∠B are supplementary,∠B and ∠C are supplementary.
Proof: 
Statement                                                             Reason
1. Quadrilateral ABCD is a parallelogram         Given
2. AB||DC and AD||BC               Opposite sides of parallelogram are parallel
3. ∠A and ∠B are same side interior angles
and ∠B and ∠C are same side interior angles.  Definition of parallelogram
4. m∠A+m∠B=180°
and m∠B+m∠C=180°         Same side angles of a parallelogram are of 180° 
5. ∠A and ∠B are supplementary.
and ∠B and ∠C are supplementary.    Definition of supplementary angles.