Which of the following is a mechanism of action for NRTIs?

NRTIs, or nucleoside reverse transcriptase inhibitors, function by incorporating themselves into the viral DNA during the process of reverse transcription, which is when viral RNA is converted to DNA by the enzyme reverse transcriptase. Once incorporated, NRTIs terminate the elongation of the DNA chain, thus halting the replication of the virus. This mechanism is particularly effective against retroviruses such as HIV, as they rely heavily on reverse transcription for their lifecycle.

The other mechanisms mentioned are characteristic of different types of antiviral agents. For example, some agents inhibit viral protease, which is essential for processing viral proteins, while others block entry into host cells or inhibit RNA synthesis, none of which pertain to the specific action of NRTIs. Hence, the correct answer highlights the unique mechanism of action employed by NRTIs in disrupting the viral replication process by terminating DNA chain elongation.