根据短文理解完成下列各题。

C

    Shenzhen is a city in South China. It is not very big, but it has attracted people of the whole country and the whole world as well.

    Just about twenty years ago, it was only a small fishing village. There were not many people there. Most of them lived on fishing. Things have greatly changed since the 1980's. It became the first special economic zone (经济特区) in China.

    Because of the opening policy(政策), economic changes between China and the outside world have increased greatly. People can come and go easily between Shenzhen and Hong Kong. Both foreigners and Chinese have built a lot of factories, companies and tourists' attractions there. People all over the country have come to find jobs. Many of them have settled down in this new booming(兴起的) city.

    Shenzhen is developing so fast that it has become a well-known metropolis(大都市) in China.

如图1表示含有目的基因D的DNA片段长度（bp即碱基对）和部分碱基序列，图2表示一种质粒的结构和部分碱基序列．现有MspⅠ、BamHⅠ、MboⅠ、SmaⅠ4种限制性核酸内切酶切割的碱基序列和酶切位点分别为C↓CGG、G↓GATCC、↓GATC、CCC↓GGG．请回答下列问题：

（1）图1的一条脱氧核苷酸链中相邻两个碱基之间依次由____ 连接．

（2）若用限制酶SmaⅠ完全切割图1中DNA片段，产生的末端是____ 末端，其产物长度为____ ．

（3）若图1中虚线方框内的碱基对被T﹣A碱基对替换，那么基因D就突变为基因d．从杂合子分离出图1及其对应的DNA片段，用限制酶SmaⅠ完全切割，产物中共有____ 种不同DNA片段．

（4）若将图2中质粒和目的基因D通过同种限制酶处理后进行，形成重组质粒，那么应选用的限制酶是____ ．在导入重组质粒后，为了筛选出含重组质粒的大肠杆菌，一般需要用添加____ 的培养基进行培养．经检测，部分含有重组质粒的大肠杆菌菌株中目的基因D不能正确表达，其最可能的原因是____