**Core Concept**
Zidovudine and didanosine are nucleoside reverse transcriptase inhibitors (NRTIs) used in the treatment of HIV/AIDS. They exert their antiretroviral effect by inhibiting the reverse transcriptase enzyme, which is essential for the replication of retroviruses like HIV.

**Why the Correct Answer is Right**
NRTIs like zidovudine and didanosine act by incorporating themselves into the viral DNA, causing chain termination. This is because they lack a hydroxyl group at the 3' position, which is necessary for the addition of new nucleotides to the growing viral DNA chain. As a result, the viral DNA strand is terminated, and the virus is unable to replicate. This mechanism of action is specific to NRTIs, which are a class of antiretroviral drugs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the mechanism of action of zidovudine and didanosine.
**Option B:** Protease inhibitors, not NRTIs, are a different class of antiretroviral drugs that act by inhibiting the protease enzyme.
**Option C:** This option is not specific to zidovudine and didanosine and is a general mechanism of action for many antiretroviral drugs.

**Clinical Pearl / High-Yield Fact**
NRTIs like zidovudine and didanosine can cause mitochondrial toxicity, leading to side effects like myopathy and lactic acidosis. This is because they can also inhibit the mitochondrial DNA polymerase gamma, leading to impaired mitochondrial function.

**Correct Answer:** C. Inhibiting reverse transcriptase enzyme activity.