Distinguishing Simple Subject and Predicate

“Runners drink only water while training.”

Definition of a Complete Sentence
A complete sentence must have a subject and predicate and express a complete idea.
You can write a complete sentence with just two words in it: 1) a verb that expresses an action or a
state of being, and 2) a noun that performs the action. Most sentences contain additional words to give more information about the subject and predicate.

Examples:
People applauded.
The people in the audience applauded loudly at the end.

Which part of this complete sentence could also stand alone as a complete sentence?

A) Runners drink.
B) Only water.
C) While training.