A polymer consists of

Options

A. Only one monomer molecule
B. Only one type of monomer, repeating itself
C. Two types of monomers, repeating themselves
D. A number of different monomers, connected to each other

Explanation

### Step-by-Step Text Solution:

1. **Understanding Polymers**: A polymer is a large molecule made up of repeating structural units known as monomers. These monomers can be identical or different.

2. **Identifying Monomer Types**:
- **Option 1**: "Only one monomer molecule" - This does not describe a polymer because a polymer must consist of multiple repeating units.
- **Option 2**: "Only one type of monomer repeating itself" - This is a correct description of a polymer. For example, polyethylene is made from the monomer ethylene (CH2=CH2) repeating.
- **Option 3**: "Two types of monomer repeating itself" - This describes a copolymer, which is a type of polymer but not the only type.

3. **Conclusion**: Based on the definitions and options provided, the correct answer is **Option 2**: A polymer consists of only one type of monomer repeating itself.

4. **Example**: An example of such a polymer is polyethylene, where the monomer (CH2=CH2) polymerizes to form a long chain of repeating units (CH2-CH2)n.