Think of a dance floor, which is designed to dampen vibrations and limit the ( ) dancers could do to their limbs.

(单选题)What can we infer according to the text? ( ) (单选题)What can parents do according to the researchers? ( ) (单选题)What is the passage mainly about? ( ) (单选题)What can we learn from the passage? ( ) (单选题)How much sleep do the average teens need? ( ) (单选题)How many parents report their teens worry about school? ( (单选题)This new policy proved effective, leading to ( ) increase (单选题)Poor schooling was the ( ) of the unemployment problem. (单选题)One's economic condition often ( ) his or her way of life (单选题)These are defensive behavior patterns which ( ) from our