Riddles

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I am an odd number. Take away a letter and I become even. What number am I?
What occurs once in a minute, twice in a moment, and never in 1,000 years?
What invention lets you look right through a wall?
What five-letter word typed in all capital letters can be read the same upside down?
What starts with T, ends with T, and has T in it?
What is the longest word in the dictionary?