Answer:
The correct direct object pronouns that fill the blanks are:
1. Los viajeros compran <u>los</u> pasajes. Ellos <u>los</u> compran.
2. La viajera confirma <u>la</u> reservación. Ella <u>la</u> confirma.
3. El empleado tiene <u>las</u> llaves. Él <u>las</u> tiene.
4. Yo escribo una carta. Yo <u>la</u> escribo.
5. Alejandra pierde el equipaje en el aeropuerto. Ella <u>lo</u> pierde.
Explanation:
In Spanish, <em>some direct object pronouns are similar to the articles</em>, in the first three sentences I underlined the articles because those are the same word that the direct object in the contract sentence; in the fourth sentence, the article is undefined "una" but continues referencing to <em>a female object</em>, by this reason, the direct object pronoun is "la" and the last sentence, the subject "el equipaje" is <em>a male object</em>, then its direct object pronoun is "lo".