The correct answer is (B) To decrease; to decline in size, power, vigor, importance, repute, or splendor, like the moon after the full. To diminish in strength, reputation, influence, prosperity, etc. To draw to a close; to approach an end.

Wane comes from (Old English) wanian, Old Norse vana (diminish)

Examples of use:

• Attendance at church has been waning for many years.
• His interest in the case waned as the days progressed.