Which of the following are common features of expression vectors?
a. small segments of dna that encode tags for protein purification.
b. transcriptional start and stop sites
c. a tightly controlled promoter than can only be induced under certain circumstances
d. antibiotic resistance gene
e. all of the above are common features of expression vectors

Which statements best describe the differences or similarities between a comparative investigation and an experimental investigation? check all that apply. experimental investigations are best for showing cause-and-effect relationships, while comparative investigations do not necessarily show this type of relationship. comparative investigations are often impractical and unrealistic, while experimental investigations are the most practical and realistic kinds of investigations. comparative investigations allow for the use of a wide range of variables but do not have a control group, while experimental investigations involve variables that can be controlled. both experimental investigations and comparative investigations are designed to answer scientific questions. both experimental investigations and comparative investigations focus on making observations rather than collecting new data.