下列关于“观察DNA和RNA在细胞中的分布”实验的说法,正确的是( )
A:甲基绿和吡罗红对DNA和RNA的亲和力不同,实验中应分别加入甲基绿和吡罗红
B:盐酸能够改变细胞膜的通透性,加速染色剂进入细胞
C:该实验用口腔上皮细胞而不用叶肉细胞,是因为叶肉细胞不含RNA
D:盐酸有利于染色质中DNA与蛋白质分离,不利于DNA与染色剂结合
Do you still get free plastic bags from the supermarkets? Things have changed. China has banned(禁止)free plastic bags in shops and supermarkets,and people have to pay for using plastic bags. The rule started on June 1st. It came because our country tried to make less litter. Making super-thin plastic bags has also been banned. The Chinese once used about 3,000,000,000 plastic shopping bags a day,and they have caused pollution of the environment. The bags have become a main cause of plastic pollution because they are easy to break and people throw them away here and there. So the Chinese people are encouraged to bring their own bags for shop ping. What kind of shopping bag is the best to bring? Some students in Chongqing have a good idea. They make their own shopping bags. They use old clothes to make cloth bags,and send them to their parents as presents. They also ask their parents and friends to use cloth bags instead of plastic ones. They think it is their duty to protect the environment.根据短文内容,选择最佳答案。
用竖式计算。
139+257= 36×88= 756÷7=
375÷+5= 3.6+2.8= 23×45=
①食物多样,粗细搭配
②在野外采集的新鲜蘑菇,可以直接使用
③肉鱼蛋类,必须新鲜
④水果出现部分腐烂,未腐烂部分可以使用
⑤“虫眼蔬菜”,放心食用
⑥每日三餐,按时进餐