To describe a current activity while watching a class. This requires the use of the present continuous tense, which is formed by "am/is/are + verb-ing."

The correct option is A.

The question asks to describe a current activity while watching a class. This requires the use of the present continuous tense, which is formed by "am/is/are + verb-ing."

• A) "I am studying at Platzi right now." This sentence uses the present continuous tense ("am studying") and the time phrase "right now," which correctly describes an action happening at the moment of speaking.
• B) "I study at Platzi right now." This uses the simple present tense ("study"), which is typically used for habitual actions or facts, not for an action happening at this exact moment, even with "right now."
• C) "I studying at Platzi every day." This is grammatically incorrect because it is missing the auxiliary verb "am" before "studying." Also, "every day" indicates a habitual action, which would typically use the simple present tense.
• D) "I am study at Platzi every day." This is grammatically incorrect. The auxiliary verb "am" should be followed by a present participle (verb-ing) for the present continuous tense, or the sentence should be in the simple present ("I study") for a habitual action.

The final answer is $\boxed{\text{A}}$.