John didn't feel well yesterday; otherwise he ______ to see his friend off at the airport. ( )
A:came
B:would come
C:would have come
D:should be coming
云南不会发生的自然灾害是( )
如图是某手机店今年1﹣5月份音乐手机销售额统计图.根据图中提供的信息,可以判断相邻两个月音乐手机销售额变化最大的是____ .
在显微镜下观察到的数量最多的血细胞是
圆x2+y2+2x=0和x2+y2﹣4y=0的公共弦的长度为( )