**Core Concept**
Benodiazepines are a class of anxiolytic and sedative medications that act on the GABA_A receptor, enhancing the effect of the neurotransmitter gamma-aminobutyric acid (GABA). This receptor is a ligand-gated chloride channel, and benzodiazepines facilitate the flow of chloride ions into the neuron, resulting in a calming effect.

**Why the Correct Answer is Right**
The specific antagonist for benzodiazepines is flumazenil, which is a competitive antagonist at the benzodiazepine recognition site on the GABA_A receptor. This means that flumazenil binds to the same site on the receptor as benzodiazepines, but with a higher affinity, thereby blocking the action of benzodiazepines and reversing their effects. Flumazenil is used clinically to reverse benzodiazepine overdoses and in some cases of benzodiazepine-induced sedation.

**Why Each Wrong Option is Incorrect**
**Option A:** Flunitrazepam is a benzodiazepine itself, not an antagonist.
**Option B:** Diazepam is a benzodiazepine with a longer half-life and is used for its anxiolytic and sedative effects, not as an antagonist.
**Option C:** Midazolam is a benzodiazepine used for its sedative and anxiolytic effects, particularly in medical procedures, and is not an antagonist.

**Clinical Pearl / High-Yield Fact**
Flumazenil has a relatively short half-life and may need to be administered repeatedly to maintain its effects, as its action is reversed by the reuptake of benzodiazepines. This is an important consideration in the management of benzodiazepine overdoses.

**Correct Answer: D. Flumazenil**