The Solution:
Given:
A teacher randomly selected 15 students from her class. These 15 students were interviewed by a researcher.
We are required to determine whether the 15 students is a parameter or a statistic.
Recall:
A parameter is a number describing a whole population (e.g., population mean), while a statistic is a number describing a sample (e.g a sample mean).
From the above definition,
The 15 students is a statistic.
Therefore, the correct answer is [ a statistic ]