What does ob in front of a date mean?

How does rain affect the everglades national park? How were Victoria Falls formed? What is the worlds largest body of water? What layer of the rain forest does the black caiman live in? When was Curecanti National Recreation Area created? How tall is Half Dome in Yosemite National Park? What is the cathedral on London bridge called? Who owns conwy castle? When was the dames point bridge built? Who wrote ''the sand castle''? When was Silberman's Brooklyn Bridge picture taken? How many screws nuts or bolts are in a roller coaster? When did the sea lamprey come to the great lakes? What happened to the Hoover Dam? Which river did Lopamudra become? Explain why fewer plants are at the bottom of deep lakes? What was the original meaning of the Statue of Liberty? What lake is Cedar Point located on? Do planes now fly through the Bermuda triangle? Is barapani lake natural or man made?