Read the passage. Adapted passage: Researchers studying a preference for sweet food found that heredity may influence how strongly sweetness is experienced. In animal studies, receptors send signals about sweetness to the brain. Environment still matters: people who gradually reduce added sugar can become accustomed to less sweetness. Doctors caution against simply disabling a “sweet” mechanism because naturally sweet foods can also provide useful energy and nutrients. Artificial sweeteners therefore do not make the biology of taste irrelevant. What does the idiom “have a sweet tooth” mean?

1. To have pain in a tooth
2. To be especially fond of sweet foods
3. To avoid sugar completely
4. To study dentistry