The moon will inevitably ____ as the month ends.

• A. Wane
• B. Wax
• C. Grow
• D. Brighten

Answer: (A)

The main idea is how the moon’s changing phases describe its visible illumination. Waxing means the illuminated part grows—getting brighter as it moves toward a full moon. Waning means the illuminated part shrinks—getting dimmer as it moves toward a new moon. If the month ends, the cycle is moving toward the smaller, darkening phase, so the moon will wane. The other options imply increasing light—growing or brightening—or the term wax, which is used for increasing illumination, so they don’t fit the idea of the month ending.