Here's why:
* Present participle is the form of a verb used to create continuous tenses (e.g., present continuous, past continuous). It typically ends in "-ing".
* "Is" is the present tense, third-person singular form of the verb "to be".
* "Being" is the present participle of "to be".
Examples:
* Present continuous: He is being helpful.
* Past continuous: She was being quiet.