<img src="https://static.zxtiku.com/wangke/imgs/topic/bd7cc725408925f7f3cc2a6e517bf737.jpg"/><img src="https://static.zxtiku.com/wangke/imgs/topic/de86ca27f8087be0ea5ce65abadac77a.jpg"/> A. <br/> Πr2 B. <br/> 1 C. <br/> 1/Πr2 D. <br/> 0