________ of my sisters are experts in agriculture. Helping the farmers improve their farming techniques _________their duty. A. Each; are B. Both; is C. Neither; are D. None; is 答案:B一般情况下,蛋白质是不能透过细胞膜的,但在一些分泌细胞里,蛋白质分泌物是可以从细胞膜内分泌到细胞外去的.与这一过程直接有关的细胞器是( )
A、线粒体B、内质网C、高尔基体D、核糖体