Question

as exertion increases, it becomes more ______ to speak comfortably. challenging effortless convenient

Explanation:

To solve this, we analyze the context: as exertion (physical/mental effort) increases, speaking comfortably should become harder. "Challenging" means difficult, which fits. "Effortless" (easy) and "convenient" (handy) contradict the context of increased exertion.

Answer:

A. challenging