______ the farmers discovered theentrance to the secret cave in the valley—Totally by chance.

An e-mail address consists _______letters and dots and the symbol‘@’.

Must I return the book this week— No， you ______ . You can keep it for 20 days.

He telephoned me________he arrived in the city[ ]

I suppose it takes quite a lot of patience tomake a good teacher — _______It’s far more than that