A polypeptide which maintains the glucose level in blood is insulin.

Explanation

### Step-by-Step Solution:

1. **Identify the Polypeptide**: The question states that a polypeptide which maintains glucose levels in the blood is insulin. We need to confirm if this statement is correct.

2. **Define Insulin**: Insulin is a type of hormone that is classified as a polypeptide. It is composed of a chain of amino acids, which is characteristic of polypeptides.

3. **Source of Insulin**: Insulin is secreted by the beta cells located in the islets of Langerhans in the pancreas. This is an important detail as it highlights where insulin is produced in the body.

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