一个钢铁厂，炼750千克钢需要用5吨水。照这样计算，钢铁厂一天节约55吨生活用水，可以炼钢多少千克？

完形填空

    The summer vacation is the best time for students．They can go outdoors and have fun．They can go to big cities to  1，or go to the countryside to 2the beauty of nature(大自然)．

    Peter is an American middle school student and he loves 3  very much．He always travels in his country．

    This summer vacation he wants to do4．He is interested in Chinese history． 5he is flying to Beijing and Xi'an for the summer vacation．He is leaving on l2th July and 6 New York on the last day of the month．He plans 7 a fantastic vacation．During the 8，he is visiting places of interest and going shopping．At night，he is  9  to enjoy the night views．,He is sure he will have a  10 time．

“观察DNA和RNA在细胞中的分布”实验中没有用到的试剂是（   ）