Answer:
Something that indicates or fixes a limit or extent. Those two trees mark the boundary of our property. The mountain range that forms the country's northern boundary.
Explanation:
It is one of these meanings because I don't know what type of boundary you mean.
Answer:
I think a because fossils do stay for a very long time ribbit
I think the cytoskeletal protein that helps a cell maintain its shape is actin.
The answer is DNA which cods for spesific protein