Which of the following conditions is characterized by progressive weakness, the presence of Ach-receptor antibodies, and is more common in individuals aged 20-30 to 70-80 years old?
A) Myasthenia Gravis (MG)
B) Amyotrophic Lateral Sclerosis (ALS)
C) Guillain-Barré Syndrome (GBS)
D) Muscular Dystrophy (MD)