What two issues with fresh bedding can staff easily identify when changing cages?

The correct choice highlights the presence of foreign materials and excessive dust as two easily identifiable issues with fresh bedding when staff are changing cages.

Foreign materials may include objects such as uneaten food, hair, or fecal matter that could have inadvertently contaminated the bedding. Recognizing the presence of these materials is critical, as they can affect the cleanliness and hygiene of the environment for the animals. Additionally, excessive dust is an important concern; it can pose respiratory issues for both the animals and the handlers. Dust particles could trigger allergies or other respiratory conditions, making their identification crucial during routine bedding changes.

While other options mention important factors such as moisture buildup and odor, these issues may require more time to detect and may not be as immediately visible as the presence of foreign materials and dust. Color change and heat retention, while they might indicate different issues, are less likely to be directly linked to the quality of new bedding compared to the straightforward identification of foreign materials and dust.