决定疮疡的发展和转归的是：（）
A.阴阳盛衰
B.疮疡病期
C.发病部位
D.正邪交争
E.发病年龄
参考答案：D
_____ is no doubt ______ you have to remain seated and fasten your seatbelt before the plane lands.
A．There; whether
B．It; that
C．There; that
D．It; whether
如果数列{an}满足a1，a2-a1，a3-a2，…，an-an-1是首项是1，公比为3的等比数列，则an=______．
