DNA polymerase is an enzyme, most of enzymes function ir best at  body temperature. During process of DNA amplification/genetic engineering ,PCR,  temperature may increase to around 60${}^o$C, leading to denaturation of enzyme. Therefore, a rmostable DNA pol is used during amplification

• r-DNA technology is process involving introduction of a foreign piece of DNA containing a gene of interest into genome of an organism.
• Isolation and separation are steps in process in which various techniques are used to separate required gene (containing gene of interest) from nucleus of cell (free of or cellular contaminants).
• The isolated DNA is n restriction digested and amplified to make several copies. 
• It is n inserted into a vector for transfer into an appropriate host. 
• Elution is a step involved in process of separation of DNA. 

Transposon tagging refers to molecular isolation of transposable elements from genes in which element resides. It is done by identification a mutant plant stock in which mutation is because of insertion of transposable element into gene, creation of its genomic library followed by screening of library with a clone for transposable element. The selected clones have mutated gene lying adjacent to element and are used to develop subclone containing gene sequences. This clone is n used to screen a genomic library containing DNA from a normal plant. Transposon tagging has been done in maize and fruit fly using class II transposons which are characterized by presence of inverted repeats at ir ends and ability to synsize transposase. Class I transposons are abundant in human genome which are tagged for gene cloning. The correct answer is D.

When Ampicillin sensitive bacteria are exposed to plasmid containing gene for resistance, all sensitive strains will be now insensitive or resistant to Ampicillin, when grown on  nutrient media with and without ampicillin, both will be having colonies of ampicillin resistant bacteria as sensitive form has been converted to resistant form prior to segregating in growth plates.