Since there are no answer choices listed, potentially because this is an open-ended type question, I am just going to list a couple of possible ways to contract gastroenteritis. Welp, here goes nothing - I guess:
Gastroenteritis can be contracted through shellfish that have been contaminated by sewage. It can also be contracted through food handlers and/or food preparers that already have gastroenteritis; this is especially likely of happening if they have poor kitchen hygiene and don't wash their hands regularly.
Fun Fact: Having trouble spelling gastroenteritis? Here's a little fun way to remember it that I made up myself! Gastroenteritis can be split up into the following three parts: gastro - enter - itis. This is just a little Easter Egg that makes remembering gastroenteritis's spelling a whole lot easier!