Answer:
Yo compré la entrada en el mostrador el la línea aérea.
Explanation:
It would be the third option (Yo compré la entrada en el mostrador el la línea aérea.)
It's not the first one because "compré" needs an accent mark.
It's not the second one because comprí (to my knowledge as a Spanish speaker) is not an actual word.
The third option is correct.
