C = _________________ D = ______________ E = ________
四、简答题（回答要点,每小题4 分，共五小题，共20分）
28 When you study the DNA components of phage ΦΧ174, you get the results as follows: A，25%；T，33%；G，24%；C，18%. Question (1): Does your results abide by base pairing rules? Question (2): How do you explain your results?
29. DNA ligase plays important role in the process of DNA replication, but ligase does not function in the process of RNA synthesis. Could you explain it? 30 Do you think that rRNA and tRNA are more stable than mRNA? Why? 31. How does a coding region DNA sequence code different types of protein? 32. Could you list 4 kinds of RNA that have the ability to catalytic activity?
五、问答题（每小题10 分，共20分）。
33. Please tell us the types of RNA that you know, it would be better that you explain their function in living organisms. (10 points )
34. Take the case of arabinose operon, Could you explain what cis-acting element and trans-acting factor are, how do they interact with each other to regulate this operon? (10 points )
六、分析题（每小题10 分，共 10 分） 35. A scientist got a gal promoter mutant E.coli.which can not use galactose(半乳糖) in the medium, if he mutated the gene cya (gene of cAMP 环化酶) and crp (cAMP Acceptor Protein gene) were mutated into cya- and crp- respectively, the second mutated E.coli.restored its ability to use galactose. Could you explain the results by using your molecular biological knowledge?