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____ 

阅读下面材料，在空白处填入适当的内容（不多于3个单词）或括号内单词的正确形式。

Dear Tom，

    How time flies! You ____ (study) in Beijing for nearly a month, during which you must have achieved a lot. Well, how's everything going? It is reported that the weather there is very hot and dry these days, which is very different from____ of your country. Have you adapted to it? In addition, you once complained that the food ____ (serve) there was not ____ your taste. I hope that should have been improved.

    I am glad to tell you that I will go to Beijing to take part in an English speech contest in July, ____ is not only an honor, but also a great opportunity for me to improve ____. And now I try my best to make ____ (prepare) for it. ____, I have some trouble in collecting the materials relevant and using the language. I will appreciate ____ if you give me a hand to solve the problems.

    After the contest, I am to drop ____ at your school to visit you. Please wait for my phone.

Li Hua