The Market for Good X Consists of Only Two Consumers; $\ge$

The market for good X consists of only two consumers; their demand curves are given by Q = 10 - 0.10P and Q = 5 - 0.10P. What is the market demand curve?

A) Q_M = 15 - 0.2P if P $\ge$ $50, and Q_M = 5 - 0.10P if P < $50
B) Q_M = 15 - 0.2P if P $\le$ $50, and Q_M = 10 - 0.10P if P < $50
C) Q_M = 15 - 0.2P if P < $50, and Q_M = 10 - 0.10P if P > $50
D) Q_M = 15 - 0.2P