Final answer:
The main difference between "otro" and "otra" is that they are used to refer to a masculine or feminine noun, respectively. They change depending on the gender of the noun they modify.
Step-by-step explanation:
The main difference between "otro" and "otra" is that they are used to refer to a masculine or feminine noun, respectively. Therefore, "otro" is masculine and "otra" is feminine. They change depending on the gender of the noun they modify.
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