Riddle Of The Sphinx II: Sustained Release Riddlin'

I was driving down to LA when the cops pulled me over. "You have to turn back sir, the Sphinx here eats any traveler who can't answer her riddle."

"I've trained my whole life for this" I said, and stepped on the gas. Soon I saw a Sphinx lounging in the middle of the road. When she spotted me, she asked: "What has braces, crowns, and retainers, but is not teeth?" "A medieval king in armor. My turn. What has pupils, irises, and whites, but is not an eye?"

"A gardening class during apartheid. How is a river like the Federal Reserve?"

"It maintains liquidity despite rushes on the banks. What has wings, but cannot fly - fins, but cannot swim - and heels, but cannot walk?"

"Helsinki General Hospital." The Sphinx licked her lips. "But tell me, how is Lord Nelson like a cigar?"

"They both have one I and won sea. How is Mary Mary Quite Contrary like the Norse god Odin?"