Pick up the correct statement from the following: A. The substance which consists of one primary chemical, is known as monomer B. The polymer consists of thousands of monomers joined together C. The polymer molecule is called macro-molecule D. All the above

The correct answer is D. All of the above.

A monomer is a small molecule that can be linked together with other monomers to form a polymer. A polymer is a large molecule that is made up of many monomers. A macro-molecule is a very large molecule, and polymers are examples of macro-molecules.

For example, polyethylene is a polymer that is made up of many ethylene monomers. Ethylene is a small molecule with the formula $C_2H_4$. Polyethylene is a large molecule with the formula $(C_2H_4)_n$, where $n$ is a large number.

Polymers are found in many different materials, including plastics, rubber, and textiles. They are also found in living things, such as proteins, DNA, and RNA.