Answer:
Although the sensory systems associated with these senses are very different, all share a common function: to convert a stimulus (such as light, or sound, or the position of the body) into an electrical signal in the nervous system. This process is called sensory transduction.
I believe the answer is: 4. They require a large sample size.
The data required in a longintudinal study is taken by examining the sample population for a long period of time, as they develop over the years. The amount of population in such studies is usually really small, but the amount of time needed for start to finish is the one that become the main problem among researchers
