Answer:
This type of sample can be best described as a stratified sample
Explanation:
Samples may be classified as:
Convenient: Sample drawn from a conveniently available pool.
Random: Basically, put all the options into a hat and drawn some of them.
Systematic: Every kth element is taken. For example, you want to survey something on the street, you interview every 5th person, for example.
Cluster: Divides population into groups, called clusters, and each element in the cluster is surveyed.
Stratified: Also divides the population into groups. However, then only some elements of the group are surveyed.
In this question:
The students are divided into groups, according to how many years they have attended the university. Then, from each group, some(30) students are surveyed. This is an example of Statrified Sampling