What begins with T, ends with T, and has T in it?

Which alphabet is a part of our body?

Prove that twice of ten is the same as twice of eleven.

When does a USA Potato change its nationality?

What does a man do only once in his lifetime, but women do once a year after they are 29?

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?

What is the fastest way to double your money?

What's the only room from which no one can enter or leave

How is a fly different from a mosquito?

Rearrange the letters in "new door" to make one word.