Everyone was silent as the judge ____ (宣布) the winner of the competition.
I can't find ________ beef in the fridge. Shall I buy some?
已知有理数a、b、c在数轴上对应的位置如图所示,那么下列式子错误的是( )
洋葱表皮细胞在低倍显微镜下的物像和在高倍显微镜下的物像相比,前者( )
以下细胞结构中不具有膜结构的细胞器是 ____
(①核糖体、②细胞核、③线粒体、④内质网、⑤高尔基体、⑥叶绿体、⑦中心体)