Fill in the blanks.
a. Angle forming a linear pair are __P__ angles.
b. The angle between the bisectors of the two acute angles of a right-angled traingle is __Q__ .
c. Sum of interior angles of a quadrilateral is __R__
| P | Q | R | |
| A | Supplementary | 135° | 360° |
| B | Complementary | 135° | 720° |
| C | Supplementary | 90° | 180° |
| D | Complementary | 90° | 360° |
answer should be c