Final answer:
Mr. Lu tries to use a selection of food items, which may be 'spiked' with bacteria, to give the class their test. The students may also include items of interest in the food samples they transport to the lab.
Step-by-step explanation:
The food that Mr. Lu tries to use to give the class their test is a selection of food items such as ground beef, bagged lettuce, eggs, chicken, etc.
These food items may be 'spiked' with bacteria to simulate a contaminated food sample for testing.
The students may be encouraged to include items of interest that they transport to the lab with them.