The people were skeptic about aliens and UFO's because they don't believe in them.
"The people were skeptical when the scientist told them that his son was taken by extraterrestrials."
I am skeptical about the probability that birds can travel to the moon. The police officer was skeptical of her answer, therefore he chose to give her a lie detector test.
Sometimes I am skeptical about the weatherman because sometimes they are wrong about the forecast.
That skeptical school work was preety hard