# "I'm (just) not sure" | "I (just) don't know" | "I (just) don't think"
# "" | "about this" | "(if) this is (such) a good idea"

I'm not sure.
I'm not sure about this.
I'm not sure this is a good idea.
I'm not sure if this is a good idea.
I'm not sure this is such a good idea.
I'm not sure if this is such a good idea.

I don't know.
I don't know about this.
I don't know this is a good idea.*
I don't know if this is a good idea.
I don't know this is such a good idea.*
I don't know if this is such a good idea.

I don't think.*
I don't think about this.*
I don't think this is a good idea.
I don't think if this is a good idea.*
I don't think this is such a good idea.
I don't think if this is such a good idea.*

Are you sure?
Are you sure about this?
Are you sure this is a good idea?
Are you sure if this is a good idea?
Are you sure this is such a good idea?
Are you sure if this is such a good idea?

Do you think?*
Do you think about this?*
Do you think this is a good idea?
Do you think if this is a good idea?*
Do you think this is such a good idea?
Do you think if this is such a good idea?*