You're French. ----- REALIZE
I didn't realize (that) you're French.
What do you mean? ----- UNDERSTAND
I don't understand what you mean.
Will I live to be 100? ----- DOUBT
I (very much) doubt that I will live to be 100.
Will it rain tomorrow? ----- WONDER
I wonder if it will rain tomorrow.
Is it 5 o'clock already? ----- BELIEVE
I don't believe it is 5 o'clock already!
Where did I leave my keys? ---- KNOW
I don't know where I left my keys.
How did the story end? ----- FIND OUT
I never found out how the story ended.