Bill is setting his cup on a table. He puts a napkin under it to avoid leaving what?\nOptions:\n- noise\n- knocking over\n- put down\n- doesn\n- water mark
A step-by-step solution is:
water mark
Napkin can avoid a watermark by a cup.

Cup may cause watermark if a napkin is not used under it.

.

Therefore, the answer is water mark