单项选择。
当你不认识某物时,应该用英语向别人问:( )
答案:A
下列关于DNA和蛋白质提取与分离实验的叙述,正确的有[ ]
A.提取细胞中的DNA和蛋白质都需用蒸馏水涨破细胞
B.用不同浓度NaCl溶液反复溶解与析出DNA可去除蛋白质
C.蛋白质提取和分离过程中进行透析可去除溶液中的DNA
D.蛋白质和DNA都可以用电泳的方法进行分离纯化
The table above gives the gasoline costs and consumption rates for a certain car driven at 50 miles per hour, using each of two brands of gasoline. How many miles further can the car be driven at this speed on $12 worth of brand X gasoline than on $12 worth of brand Y gasoline ?()
A.20
B.24
C.84
D.100
E.104