题干
When I walked past the park, I saw some old people _________ Chinese Taiji.
A：do
B：did
C：doing
D：are doing
答案(点此获取答案解析）
C
When I walked past the park, I saw some old people _________ Chinese Taiji.
A：do
B：did
C：doing
D：are doing
=1（a＞0，b＞0）的一条渐近线，则该双曲线的离心率为