The correct answer is (A) To move in waves; to have or cause a smooth, wavelike or sinuous motion or form; to move with a smooth rising and falling, or side-to-side motion; to have a wavy form.

Undulate comes from Latin unda (wave)

Examples of use:

• The flag undulated in the breeze above the clubhouse.
• A snake undulated across the grass a few feet away while they spoke.