a. is correct and the following explanations give you the info:
a) Interval data is not only a rank but also has meaningful intervals between scale points. Do Likert data qualify as interval
measurements? By choosing the verbal anchors carefully many researchers believe that the intervals are the same (e.g., the distance from 1 to 2 is “the same” as the interval, say, from 3 to 4).
b) Cross-sectional data are data that are collected from participants
at one point in time. Time is not considered one of the study variables in a cross-sectional research design
c) A census is an attempt to gather information from each and every person of interest – the universe of study targets. A sample gathers information from only a part or subset of the universe of possible participants. If a researcher has relatively few
actual (and potential) customers, let’s say owners of million dollar yachts, he can afford to take a census – attempt to contact all of them. However,
if the number of customers is in the thousands or millions, a census is much too expensive and sampling provides a very good alternative.
True, a sample is always only an estimate and is subject to sampling error. But the larger the sample (and consequently the cost) the more accurate the findings will be. The research can then determine a mix of cost and accuracy that is acceptable.
In addition, samples are not always less accurate than a census.