—They keep their hands on the phones wherever they go, even while they _______ meals.
如图所示,当开关S闭合后,电压表测出的电压是( )
下列关于世界气温分布的叙述,不正确的是( )
用墨汁将细菌染色后放入草履虫培养液中,用显微镜观察草履虫,发现黑色结构是( )