Answer: A. 30 students in the lunchroom.
Step-by-step explanation:
A representative sample simply refers to the sample that has same characteristics just like the population.
A random-based selection is regarded as a representative of the population. In this case, the random sample that represents a representative sample of the number of students who enjoy science class is "30 students in the lunchroom".
When the students in the lunchroom are chosen, then it's a representation of the entire students in the school. This is the best option when compared to other options as they don't represent the students entirely.