A:an underground lake was discovered
B:workers discovered an underground lake
C:there was an underground lake discovered
D:a lake was discovered underground
已知x1,x2是关于x的一元二次方程ax2+bx+c=0的两根,若x1<1<x2,则x1+x22+x12x22 的取值范围是( )
根据首字母填写单词。
下列属于单细胞动物的是( )
若x﹣y=8,xy=10.求x2+y2的值.