1. Right answer:
a los
We choose a los because the noun juegos is given in masculine plural form. So definite article must match the noun they modify in both gender and number. Hence we conclude that los is the definite article given in masculine plural form. On the other hand, this sentence is given in simple present because the verb jugar is conjugated as juega that matches the formal you (usted). Finally:
Usted juega muy bien a los juegos de mesa.
2. Right answer:
a los
As in the previous exercise, in this problem we have that videojuegos is a masculine plural noun. This exercise is a question, so in Spanish is valid that you start this question either as ¿juegan ustedes... or ¿ustedes juegan... This sentence also stands for the simple present and the verb jugar is conjugated matching the second person plural (ustedes). Finally:
¿Juegan ustedes a los videojuegos?
3. Right answer:
juegan
This sentence stands for the simple present. Since Los muchachos can be replaced by ellos, then we need to conjugate the verb jugar matching the third person plural in the simple present, which is juegan. It's important to say that the simple present tense is used to talk about habitual actions or routines. This tense is also used to describe things that happen now or in the near future.
Los muchachos juegan al fútbol los sábados.
4. Right answer:
jugamos
This sentence also stands for the simple present. Since Anita y yo (that translates into Anita and I) can be replaced by nosotras, then we need to conjugate the verb jugar matching the first person plural in the simple present, which is jugamos. So ellas is given in feminine plural form. Finally:
Anita y yo jugamos al tenis después de clases.
5. Right answer:
juegas
This sentence also stands for the simple present. Since we use the subject pronoun for the second person singular, which is tú, then we need to conjugate the verb jugar matching the second person singular in the simple present, which is jugas. Finally, we can write this sentence as follows:
¿A qué deporte juegas tú?