已知如图，圆柱OO₁的底面半径为13cm，高为10cm，一平面平行于圆柱OO₁的轴OO₁，且与轴OO₁的距离为5cm，截圆柱得矩形ABB₁A₁，则截面ABB₁A₁的面积是（　　）

①树立协作、互助的合作观念

②反对不正当竞争

③彻底击垮竞争对手

④在竞争中合作，在合作中竞争

Rt△ABC中，∠C=90°，若AB=a，∠A=θ，则AC的长为（       ）．

· Finding：Seniors, on average, bathe fewer than 3 times a week. And nearly 30% wash their hands only 4 times a day - half of the number doctors advise.

· Step：We touch our faces around 3,000 times a day - often inviting germs（病菌）to enter our mouth, nose, and eyes. Use toilet paper to avoid touching the door handle. And, most importantly, wash your hands often with hot running water and soap for 20 seconds.