A:He is from America.
B:He speaks English well.
C:He is kind and strong.
D:He is my best friend.
(1)已知分式2x2-8x-2,x取什么值时,分式的值为零?
(2)x为何值时,分式x2+23x-9的值为正数?
下列关于遗传学知识的叙述,正确的是( )