Correct Answer: Plain

Solution : The third option is the correct choice.

Bombastic refers to language that is marked by extravagant and pompous expressions, often used to impress or exaggerate. On the other hand, plain suggests simplicity and straightforwardness, lacking embellishment or elaborate language.

The meanings of other options are as follows:

• Essential means absolutely necessary or fundamental.
• Sarcastic means using irony to mock or convey contempt.
• Rhythmic means having a regular and repeated pattern, especially in sound or movement.

Therefore, the correct answer is plain.