<span>1 archaic : happy, pleased
2 archaic : inclined, desirous
3 a : willing
he was very fain, for the young widow was “altogether fair and lovely … ” — Amy Kelly
b : being obliged or constrained : compelled
Great Britain was fain to devote its whole energy … to the business of slaying and being slain — G. M. Trevelyan</span>
Answer:
So they ate the food before the parents could come home
Explanation:
C. uses
Uses is the only word that words in this context. The advertisement isn't keeping anything. It hopefully creates a desire in the consumer to buy a product but it doesn't create a technique. It also does intend to convince buyers but it can't intend a technique either. Techniques are used so this is the most accurate and precise replacement for has.