one sample on one rainy day. one sample a day on several rainy days. several separate samples on one rainy day. several separate samples on several rainy days.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Betsy wants to find out if the rainfall in her town contains pollutants. The best way for Betsy to gather this information would be to collect
Possibilities:
- one sample on one rainy day.
- one sample a day on several rainy days.
- several separate samples on one rainy day.
- several separate samples on several rainy days.

several separate samples on several rainy days.