A label for slightly toxic pesticides must carry which of the following words?

The correct designation for slightly toxic pesticides is to carry the word "Caution" on their labels. This term indicates a lower level of toxicity compared to other classifications, serving as a warning to users to handle the pesticide with care, but not implying immediate or severe danger.

In the classification system for pesticide toxicity, "Caution" is utilized for products with the least potential to cause harm. On the other hand, "Warning" typically indicates a higher level of toxicity and "Danger" signifies the highest toxicity, indicating that immediate harm is possible if not used safely. "Alert" is not a standard term used in this context and does not convey the necessary information about toxicity levels. Thus, "Caution" accurately reflects the intended safety message for slightly toxic pesticides.