A person chooses one bus route from 2 routes and one train route from 5 routes. How many total choices are possible?

Correct answer: 10 choices

The governing concept is the fundamental principle of counting, also called the multiplication rule. A complete outcome requires two selections: one bus route and one train route. There are 2 choices for the bus route, and for each of those choices there are 5 independent choices for the train route. Thus the number of ordered bus-train pairs is 2 × 5 = 10. Therefore option D is correct. Adding 2 and 5 to obtain 7 would be appropriate only if the person chose one item from either category, not one from both. The answer 5 ignores the bus selection, while 20 has no basis in the stated two-stage process. Each pair represents one complete travel choice.