Answer:

Explanation:
An element only has <u>one</u> type of atom and cannot be broken down by chemical means.
Let's analyze the answer choices.
1. This has two types of atoms, so it cannot be an element. It has more than one type of atom.
2. This has two types of atoms that are bonded together. It cannot be an element because there is more than one type of atom and the bonds can be broken.
3. This has one type of atoms, so it is an element.
Therefore the best answer choice is 3.
Answer:
External factors include physical and chemical signals. Growth factors are proteins that stimulate cell division. – Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells.
Explanation:
From Google
A chromosome is a Deoxyribonucleic acid molecule with part or all of the genetic material of an organism.