若有float x; int a,b; ,下面四条switch语句中正确的有( )条。switch(x){ case x=1.0: printf(“Y”); case x=2.0: printf(“N”); }switch(a){ case a=1: printf(“Y”); case a=2: printf(“N”); }switch(b){ case b==1: printf(“Y”); case b==2: printf(“N”)௲垎뗐敔敔垎�敘垎၈Ǔ瘓礀Ǡ㰰Ǒ㰰Ǒብ盂撮௬Ѐ