1. C Since angles in a triangle add to $180^{\circ}$ and one angle is given as $90^{\circ}$, the two blank angles in the triangle add to $90^{\circ}$. Since angles on a straight line add to $180^{\circ}$, the sum of the two marked angles and the two blank angles in the triangle is $2 \times 180^{\circ}=360^{\circ}$. Therefore the sum of the two marked angles is $360^{\circ}-90^{\circ}=270^{\circ}$.
1. The triangle in the diagram contains a right angle. What is the sum of the other two marked angles on the diagram?
A $150^{\circ}$
B $180^{\circ}$
C $270^{\circ}$
D $320^{\circ}$
E $360^{\circ}$