## Nine cities served by two competing airlines

**Problem**

There are nine cities which are served by two competing airlines. One or the other airline (but not both) has flight between every pair of cities. What is the minimum number of possible triangular flights (i.e., trips from *A* to * B* to C and back to A on the same airline)?

A. 12 | C. 10 |

B. 14 | D. 16 |

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