Great changes __________ in my hometown since 1990.
A:have been taken place
B:have taken place
C:take place
D:had taken place
等差数列{an}中,a3和a9是关于x的方程x2﹣16x+c=0(c<64)的两实根,则该数列前11项和S11=( )
在△ABC中,内角A,B,C所对的边分别是a,b,c.若a=ccosB,则△ABC是( )