A7. A straight angle is divided into four angles by three rays, the sizes of which are in the ratio $1: 2: 5: 1$. What is the measure of the largest angle?
(A) $20^{\circ}$
(B) $50^{\circ}$
(C) $100^{\circ}$
(D) $200^{\circ}$
(E) $270^{\circ}$