Answer: C: Todos los dias.
Explanation: The sentence is:
"Lavarse los dientes"
The translation would be:
"brushing your teeth"
And the options are:
a) Jamas (never)
b) A veces (sometimes)
c) Todos los dias (every day)
The option that best completes the sentence is option c, every day because you should brush your teeth every day, so the answer is option c "todos los dias"