Correct the statements
Hydrogen is used as a fuel for rocket propulsion.

Explanation

**Step-by-Step Solution:**

1. **Identify the Statement to be Corrected:**
The original statement is: "Hydrogen is used as a fuel for rocket propulsion."

2. **Specify the Type of Hydrogen Used:**
The statement needs to be corrected to specify that it is "liquid hydrogen" that is used as a fuel for rocket propulsion. This is important because hydrogen can exist in different states (gas, liquid, etc.), and for rocket propulsion, the liquid form is utilized.

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