Simplify the following text for a Grade 13 native English-speaking person.
Original: The museum has many rare and important aircraft and other exhibits , including one of four surviving Convair B-36s , the only surviving XB-70 Valkyrie , and Bockscar -- the B-29 Superfortress that dropped the second atomic bomb in World War II .
Simplified: Included in the permanent collections are one of four surviving Convair B-36s , the only surviving XB-70 Valkyrie , and Bockscarâ '' the B-29 Superfortress that dropped an atomic bomb on Nagasaki during the last days of World War II .