C:甲和丁
A:甲和乙
B:甲和丙
D:丙和丁
一What does your sister usually do on Saturday mornings?一She often practices English for half an hour.
Mr. King is _______ teacher I've met.
双曲线 x2a2−y2b2=1 (a>0,b>0) 的渐近线为正方形OABC的边OA,OC所在的直线,点B为该双曲线的焦点。若正方形OABC的边长为2,则a=____.