An audience of 20-year-olds finds a series of rude jokes highly amusing. A group of 50-year-olds finds the same jokes highly offensive. It is concluded that, as people age, their senses of humor become more rigid and narrow. The major difficulty in drawing conclusions of this sort is that C Longitudinal studies cannot distinguish between age differences and cohort differences O b. Cross-sectional studies cannot distinguish between age differences and cohort difference O C. Longitudinal studies cannot control for confirmation bias d. Cross-sectional studies cannot control for confirmation bias