Explanation:

- The correct phrase is "superior to." This is a common construction in English when comparing something as better than something else. Therefore, "Hitler believed that the Nordic Aryan race was superior to all other races" is grammatically correct.

- Option 1: "than" is typically used in comparative constructions like "better than," not directly after "superior."

- Option 3: "in" would indicate a position or a state within something, which doesn’t fit the context here.

- Option 4: "from" indicates a source or origin, which also doesn't align with the comparative nature needed here.