Which is correct statement?

Options

A. Starch is polymer of `alpha`-glucose
B. Amylose is a component of cellulose
C. Proteins are composed of only one type of amino acid
D. In cyclic structure of fructose, there are four carbons and one oxygen atom

Answer

To solve the question "Which is the correct statement?", we will evaluate each of the provided options one by one.

### Step-by-Step Solution:

1. **Evaluate Option A: "Starch is a polymer of alpha glucose."**
- Starch is indeed a polysaccharide made up of many glucose units. Specifically, it is composed of alpha glucose units linked together by glycosidic bonds. Therefore, this statement is **correct**.

2. **Evaluate Option B: "Amylose is a component of cellulose."**
- Amylose is actually a component of starch, not cellulose. Cellulose is made up of beta glucose units. Therefore, this statement is **incorrect**.

3. **Evaluate Option C: "Proteins are composed of only one type of amino acid."**
- Proteins are made up of various amino acids, not just one type. There are 20 different amino acids that can combine in various sequences to form proteins. Therefore, this statement is **incorrect**.

4. **Evaluate Option D: "In the cyclic structure of fructose, there are four carbon atoms and one oxygen atom."**
- The cyclic structure of fructose contains five carbon atoms and one oxygen atom in the ring. Additionally, fructose has two carbon atoms that are outside the ring. Therefore, this statement is **incorrect**.

### Conclusion:
The only correct statement among the options provided is **Option A: "Starch is a polymer of alpha glucose."**