Final answer:
Crust can neither be separated nor combined. It can only be physically divided into smaller pieces.
Step-by-step explanation:
The correct answer is d. separated; combined. Crust can be physically separated into smaller pieces, but it cannot be destroyed or combined in a way that changes its fundamental properties. For example, if you break a slice of bread into crumbs, the crust is still present but in smaller pieces. Similarly, if you combine multiple crumbs together, they do not form a cohesive solid crust. Therefore, neither 'separated' nor 'combined' accurately describes what can happen to crust.
Learn more about Crust and its properties