Enzymes that remove nucleotides one at a time from the end of a DNA molecule are called（）
A. Ligases
B. Exonucleases
C. Endonucleases
D. Modifying enzymes
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Choose the correct statement for the infectious particle of lambda phage（）
A. It is single stranded genome
B. It is circular double stranded genome
C. The ends are blunt with cos （cohesive） sequences
D. The cos （cohesive） sticking ends are created by cleavage at cos sites during phage packaging
Which of the following is correct with respect to caesium chloride centrifugation（）
A. Caesium is light in weight
B. The dissolution of caesium and nucleic acids leads to the formation of gradients
C. According to the amount of supercoiling and A+T content, the DNA settles
D. Nicked DNA settles below than supercoiled DNA
Please select the true statement（s） using vectors to make recombinant DNA（）
A. The DNA of interest could not replicate if it were not in a plasmid
B. The vector prevents degradation of DNA by phages
C. Vectors are more well-characterized than chromosomal DNA
D. They accept longer DNA fragments
Chromosomal or genomic DNA is separated by______（）
A. Sedimentation
B. Dissolution in water
Centrifugation
Distillation
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