—Yes,________.
A:these are
B:they're
C:they are
D:those are
设直线3x+4y-5=0与圆x2+y2=4相交于A,B点,则弦AB的长等于( )
①供不应求 ②互补品需求量会有所减少
③替代品需求量会有所减少 ④生产规模可能会扩大