What is the two-letter postal abbreviation for Alabama?

Whose presidential library is located in Atlanta, Georgia? Whose presidential library is located in Boston, Massachusetts? Whose presidential library is located in West Branch, Iowa? Whose presidential library is located in Ann Arbor, Michigan? Which state uses the postal abbreviation "AL"? Montgomery is the capital of which state? In what year was Alabama admitted to the Union as a state? Which state is nicknamed the "Yellowhammer State"?