“海带炖排骨”和“紫菜蛋汤”是人们喜爱的佳肴,你知道海带和紫菜与下列哪种植物同属一类吗?( )
A:水绵
B:蕨
C:白菜
D:葫芦藓
—Look! All students in the classroom are preparing for the coming exams_____.
—Yes, the exams are very important to them.
①肺泡数量多②肺泡外有丰富的毛细血管 ③肺泡壁薄④肺泡很大
从长度分别为3、5、7、9的4条线段中任取3条作边,能组成三角形的概率为( )
如图,在直角坐标系中,四边形OABC是直角梯形,BC∥OA,⊙P分别与OA、OC、BC相切于点E、D、B,与AB交于点F.已知A(2,0),B(1,2),则tan∠FDE=____.