Final answer:
The most likely answer is Myasthenia gravis (Option A) due to the combination of symptoms mentioned.
Step-by-step explanation:
The symptoms of anterior mediastinal mass, diplopia, and dysarthria can be indicative of different conditions, but in this case, the most likely answer is Myasthenia gravis (Option A).
Myasthenia gravis is an autoimmune disorder where circulating antibodies block the nicotinic acetylcholine receptors on the neuromuscular junction's motor endplate. This blockage leads to muscle weakness and fatigue, starting with symptoms like drooping eyelids and progressing to overall muscle weakness. In advanced cases, it can affect the muscles controlling breathing, leading to a myasthenia crisis.
Options B, C, and D (Thymoma, Lymphoma, and Aortic aneurysm) do not typically present with the combination of symptoms mentioned in the question.