设有如下语句:CREATETABLEtb_booking(numINTNOTNULLAUTO_INCREMENTPRIMARYKEY,cnoCHAR(10)NOTNULL,rnoCHAR(10)NOTNULL,scheduleSDATETIMENULL,scheduleEDATETIMENULL,currentdateDATETIMENULL,FOREIGNKEY(cno)REFERENCEStb_customer(cno),FORE
A. cno是tb_booking表的外键
B. cno所参照的表是tb_customer
C. 主键是num
D. num值由系统自动生成,不能手工输入