One of the primary benefits of a survey is that they a. can generate cause-and-effect conclusions b. allow efficient gathering of unobservable phenomena c. allow for researchers to observe one’s natural behavior d. are able to provide a detailed look at a single subject

I believe the answer is: b. allow efficient gathering of unobservant phenomena

Survey is conducted by letting the subject to fill up a set of questionaires by their own without the supervision of the researchers. Because of this, gathering needed information became extremely efficient since it can be conducted with very little labor resource and could take up large number of population.

is there a year set? the question is incomplete

answer; lewis henry morgan;