Compositional layers are determined by their components, while mechanical layers are determined by their physical properties.
It's called chemical reaction.
(I'm not real sure)
Answer: B. providing access to objects that are hard to find
Explanation: A specimen can be simply refered to as a sample of blood, tissue, fluid or a piece of a matter which scientist take or obtain to have a better look (study) at it in a lab.
Specimen collection is the process involved in getting or obtaining these samples for better analysis in a lab. This process help scientist get, obtain or have access to samples or objects that are not easily accessible.
Therefore Specimen collection helps scientist carry out experiment by providing access to objects that are hard to find.
