Question

where can helpful bacteria be found? (there may be more than one answer)
yogurt
skin
digestive tract
(additional options as visible but main text extracted)

Explanation:

• Yogurt: Contains probiotics (helpful bacteria) like Lactobacillus.
• Digestive tract: Human gut has beneficial bacteria aiding digestion.
• Skin: Some bacteria on skin help protect from harmful microbes. (Note: "Sun" and "Computer" are not sources of helpful bacteria.)

Answer:

• Yogurt
• Digestive tract
• Skin