Spot the differences!
This looks difficult. This is probably difficult. ...I wonder if it's difficult?
These are a series of constructions which have a somewhat similar function: they show different grades of (un)certainity about a characteristic or event. Do you know in which situation each one would be used and how much certainity it expresses?
They all revolve around a single phrase: その本が高い。
(They are all written in polite speech, except the first one. The part in bold is identical to all; just to make it easier.)