Determine whether each of the following hypotheses is testable and refutable; if not, explain why.
a. The color red as seen by males is different from the color red as seen by females.
b. A list of three-syllable words is more difficult to memorize than a list of one syllable words.
c. The incidence of paranoia is higher among people who claim to have been abducted by aliens than in the general population.
d. If the force of gravity doubled over the next 50,000 years, there would be a trend toward the evolution of larger animals and plants, which could withstand the higher gravity.