A:(kπ+π2,kπ+3π2),k∈Z
B:(2kπ−π2,2kπ),k∈Z
C:(2kπ+π2,2kπ+π),k∈Z
D:(kπ−π2,kπ),k∈Z
My grandpa's birthday is on ____(Oct. 12th/ Oct. 12nd )
天空中共有____个星座。