Riddles
100

What has many keys, but can't open a lock?

What is a piano

200

I am an odd number. Take away a letter and I become even, What number am I?

what is Seven 

300

What has many holes but still holds water?

What is a sponge

400

What occurs once in a minute, twice in a moment, but never in a thousand years?

What is the letter M

500

This thing devours all things: birds, beasts, trees, flowers. It gnaws at iron and steel. What is it?

What is time?

M
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