What is the most common way to to choose a writing topic

Does anyone know the answer to the question?

Which sentence best contrasts two things? a. air travel, like bus travel, is a fun way to get from one place to another. b. air travel is a fun and relatively easy way to get from place to place. c. both bus travel and air travel require substantial planning. d. air travel is much more expensive than bus travel.

Which example is presented in chronological