Hi As per the above comments the answer is A. We often use for + verb+ing when referring to the general use of something. So for example "PayPal is useful for buying things online." But for a specific purpose you should normally use 'to buy'. As always there are a few exceptions like "a reward for + verb+ing"

English Grammar in Use 4th ed, unit 64C. A PDF is available on the net.

"to buy" is the correct answer :) A hint: if you see the word "infinitive" it will usually have the word "to" before the verb. I hope this helps!

having to eat going to buy meaning to check intending to answer verb-ing to verb . That's English. You can find neat rules to explain that English does it like this, but basically this is the "convention called "English". This money is for buying a car. This food is for us to eat. This answer is for your understanding. noun is for reason

to buy