Final answer:
The school should survey every fifth student entering the cafeteria to get an unbiased sample of interest in soccer.
Step-by-step explanation:
In order to get an unbiased sample of interest in soccer, the school should conduct a survey that includes students from various groups and backgrounds. The best option among the given choices would be to survey every fifth student entering the cafeteria (C). This method ensures randomness and includes students from different grade levels and genders, providing a more representative sample.