A:核膜属于生物膜系统
B:染色体是遗传物质DNA和RNA的载体
C:核仁与蛋白质的合成以及核糖体的形成有关
D:核孔有利于DNA和RNA从细胞核进入细胞质
—As we know it's difficult to live in a foreign country.
—________________ if you can't understand the language there.
过圆x2+y2=4上的一点1,3的圆的切线方程是 ( )