You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: ADD A LETTER 
Clue: Confer if you wish, but if you add a letter to "confer", it becomes this type of evergreen
conifer

Category: HISTORIC EUROPEAN LEADERS 
Clue: On June 15, 1961 Walter Ulbricht assured journalists that "No one intends to build a wall" dividing this city
berlin

Category: EDUCATION 
Clue: U.S. kindergarten founder Elizabeth Peabody was the first to publish this Thoreau essay

"civil disobedience"