Reverse transcriptase is used to make cDNA from an RNA template.

A. It kills all microbes and endospores: Pasteurization does not eliminate all microbes or endospores; it reduces microbial load but is not a sterilization process.

B. It inactivates viruses: Pasteurization can reduce many viral pathogens present in milk, but the main purpose is to reduce bacterial pathogens and spoilage organisms.

C. It kills pathogenic microbes: Pasteurization is designed to inactivate or greatly reduce disease-causing bacteria (for example, Salmonella, Listeria, Mycobacterium) and extend shelf life.

D. It sterilizes the milk: Sterilization would remove all living organisms including endospores; standard pasteurization does not achieve sterilization.

A. Proteins are permanently denatured: Heat can denature proteins by disrupting noncovalent interactions; however, saying “permanently” is too absolute — some proteins may refold if conditions return to normal.
B. Membranes become too fluid for proper function: Elevated temperatures increase membrane fluidity (phospholipid tails become more disordered), impairing membrane integrity and function. This is true but incomplete alone.
C. Hydrogen bonds within molecules are broken: High temperature disrupts hydrogen bonds (and other weak interactions) that stabilize protein secondary/tertiary structure and nucleic acids; again this is true but incomplete by itself.
D. Hydrogen bonds are broken and proteins are permanently denatured: This combines two effects (bond disruption and denaturation). It’s closer, but “permanently” may be incorrect in some cases where refolding is possible — and it still omits membrane effects.
E. Hydrogen bonds are broken, proteins are denatured, and membranes become too fluid: High temperatures disrupt hydrogen bonding, cause protein denaturation, and increase membrane fluidity, all of which together explain why growth stops above the maximum growth temperature.