7. Martha draws some pentagons, and counts the number of right-angles in each of her pentagons. No two of her pentagons have the same number of right-angles. Which of the following is the complete list of possible numbers of right-angles that could occur in Martha's pentagons?
A $1,2,3$
B $0,1,2,3,4$
C $0,1,2,3$
D $0,1,2$
E 1,2
7. C The diagrams below show that it is possible to find pentagons with $0,1,2,3$ right angles. The angles in a pentagon add to $540^{\circ}$, so with 4 right angles, the fifth angle would be $540^{\circ}-4 \times 90^{\circ}=180^{\circ}$, which would make the shape flat at that vertex, thus creating a quadrilateral. Also, a pentagon with 5 right angles is not possible, because they wouldn't add up to $540^{\circ}$.