Historical clue formulations

• Source of the line "If this is the best of all possible worlds, what are the others?" — 2015-07-11
• 1956 Bernstein operetta — 2007-12-12
• *Student of Dr. Pangloss — 2007-09-26
• Classic novel that ends "Well said, but we must cultivate our garden" — 2002-09-06
• Dr. Pangloss's pupil, in Voltaire — 1999-06-23