Answer:
The correct answer is letter "D": Simple random sample.
Explanation:
The simple random sample is a term of statistics describing the most basic fundamental sample from a data population. The simple random sample is intended to represent the entire data population equivalently. Just like in the example, the data population is the 327 official ports of entry in the U.S. then the random selection is the 15 of those ports will represent the entire ports' population.