For this case we can translate the sentence given as:
_______ do not like to walk.
The sentence is given in the plural and third person, we can notice it by the word "les".
We conjugate the verb like in the present tense indicative:
yo gusto
tú gustas
él gusta
nosotros gustamos
vosotros gustáis
ellos/ellas gustan
Thus, it is observed that the correct option is "ellos".
Answer:
A ellos no les gusta pasear.
