① The trouble is that he is not at all smart.

② The question is who is going to tell him.

③ The probability is that the talks will be held before June.

④ This is where I used to work.

⑤ That is why I came here.

⑥ That is how it happened.

⑦ What do you know of the reasons for birds’ migration? All that we can say at present is that the impulse to migrate is something birds are born with.

⑧ The test of a great book is whether we want to read it only once or more than once.