**Core Concept**
The question is testing the student's knowledge of the pharmacological actions of various substances on GABA (gamma-aminobutyric acid) receptors, specifically the GABA_A subtype. GABA_A receptors are ligand-gated chloride channels that play a crucial role in inhibitory neurotransmission in the brain.

**Why the Correct Answer is Right**
GABA_A receptors are the primary target for several anesthetics, sedatives, and anticonvulsants. Substances like benzodiazepines (e.g., diazepam), barbiturates (e.g., phenobarbital), and certain inhalational anesthetics (e.g., isoflurane) act on GABA_A receptors to enhance the frequency of chloride channel opening, leading to increased inhibitory neurotransmission and sedative effects. This is in contrast to other types of GABA receptors, such as GABA_B, which are metabotropic receptors that activate potassium channels.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because benzodiazepines, such as diazepam, do act through GABA_A receptors.
**Option B:** This option is incorrect because barbiturates, such as phenobarbital, also act through GABA_A receptors.
**Option C:** This option is incorrect because certain inhalational anesthetics, such as isoflurane, act through GABA_A receptors.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that GABA_A receptors are a key target for several classes of sedatives and anesthetics, and understanding their mechanism of action is crucial for managing patients in various clinical settings.

**Correct Answer: D.**