Often Spanish adverbs are formed by using the what form of an adjective and adding suffix -mente?

You are absolutely right! Spanish adverbs are often formed by adding the -mente suffix to the feminine singular form of an adjective.

Here's a breakdown:

* Feminine singular form: To find the feminine singular form of an adjective, you'll typically add an -a to the end of the masculine singular form. For example:

* rápido (masculine) becomes rápida (feminine)

* feliz (masculine) becomes feliz (feminine)

* -mente suffix: You then add -mente to the end of the feminine singular form of the adjective. For example:

* rápida + -mente = rápidamente (quickly)

* feliz + -mente = felizmente (happily)

Important exceptions:

* Adjectives ending in -o: The masculine singular form is already the same as the feminine singular form. So, you just add -mente to the masculine form. For example:

* tranquilo (masculine) + -mente = tranquilamente (calmly)

* Some adjectives form their adverbs irregularly: There are a few exceptions where the adverb is formed differently. Examples include:

* bien (well)

* mal (badly)

* mucho (a lot)

Let me know if you have any other questions about Spanish adverbs!