This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to travel the world on $50 a day
Research what airline has the most flights out of your home airport.
Also, choose a major airline, like delta or united, that partners with international airlines to go all over the world. If you need to go to a hub to get flights, survey the cheapest connecting flights.

Pick your answer from:
a). Choose a small airport on the basis of availability. Instead of booking flights with thousands of carriers, you might want to connect your e-ticket to delta or united.;
b). Start booking autofares to and from home as early as possible. Find a city close to your home, or that has no airport.;
c). Sign up for a mileage credit card with this airline. Ensure your credit is good and that you can handle a revolving credit account.;
d). Use smartphone apps to keep track of how many tickets you earn in one day. Always remember to study websites like airfare.;
The answer is:
c).