Answer: Tomar el sol y nadar.
Explanation:
Ok, in the conversation we see that Marisa sees that Roberto has a lot of clothes, and ask him why.
He told her that he heard on the radio that the temperature was 35 degrees, and Marisa explains to him that in Mexico the scale used is Celcius, and 35 degrees Celcius is like 95 Fahrenheit, so they decide to go to the beach to swim and pass the day there.
The question is "What are they going to do at the beach?"
The only option that also appears in the text is the third one;
Tomar el sol y Nadar; that is translated to "Take a sun bath and swim"
