I _____ her not to walk on the thin ice but she would not listen to me.
How the big forest fire has ________ remains to be a mystery.
I’m waiting for the mail. Do you know _____ it will arrive?
His parents died when he was young, and he was_____ by his aunt.
–Did you plan to meet here? -- No, we met ____.
We don’t doubt _____ he will succeed in the research work.