My uncle ______ the club in 2014. He ______the club for over 3 years.
A:joined; has been a member of
B:joined; has joined
C:has joined; has joined
D:has joined; has been in
唐朝时期出现的新的生产工具是( )
请回答下列问题:
设变量x,y满足约束条件x≤2y≤xx+y≥2则目标函数z=2x+y的最小值为( )