如图表示果蝇的一个细胞，其中数字表示染色体，字母表示基因，下列叙述正确的（　　）

求：

明万历以后，江南工商业市镇之间的最大距离，一般不超过农家一日舟行往返足以完成买卖的路程。还有距离更近的，如苏州府吴江县，在明末平均约每乡3个市镇，彼此不过数里之遥。材料说明当时的江南地区（    ）

    I was only nine years old when I learnt how to use a computer．My mother is my first teacher．I know how to type，how to copy a file，and how to visit a website on the Internet．One day，mom was not at home．I turned on the computer and began to learn how to chat on net．The first one I met there was a boy called Tom．He greeted me politely．When he knew that I was only a 9-year-old girl and almost knew nothing about chatting on net，he started showing me how to use the chatting tools，how to download，and how to send e-mails．I learnt a lot from him．