I know one of the things I was unsure about was _____hard it would be to climb this mountain

k that something has to be done to stop the airfrom being polluted, ______

There is clear evidence _____ smoking does harm to our health. [ ]

Last month, our English Department invited a local radio star to _____a public lecture on the topic of mediainfluence on society. [ ]

I’d like to be on my own for a while. Do you mind–________. Go ahead.