Answer:
No están seguros de que Pedro pueda dejar de fumar.
No es evidente que estés agotado.
No creo que las medicinas naturales son curativas.
No es verdad que la cirujana quiera operarte.
Es seguro que este médico conoce el mejor tratamiento.
Explanation:
They are not sure that Pedro can quit smoking.
It is not obvious that you are exhausted.
I do not believe that natural medicines are curative.
It is not true that the surgeon wants to have surgery.
It is certain that this doctor knows the best treatment.
