Final answer:
Edrophonium is the drug used to diagnose myasthenia gravis by temporarily increasing acetylcholine levels in the neuromuscular junction, which can alleviate symptoms for diagnostic purposes.
Step-by-step explanation:
Which of the following drugs is used to diagnose myasthenia gravis? The correct answer is (D) Edrophonium. Edrophonium is a drug that temporarily blocks the breakdown of acetylcholine, thus increasing its availability in the synaptic cleft, which can briefly relieve the symptoms of myasthenia gravis. This effect can be observed clinically and helps in the diagnosis of the condition. Drugs like neostigmine and pyridostigmine also inhibit acetylcholinesterase and are used in the treatment of myasthenia gravis but are not primarily used for diagnosis due to their longer duration of action compared to edrophonium.