10.It must be admitted that you haven't done what you promised to do.
11.It is certain that we have a long way to go.
12.It is clear that the enemy has no desire for peace.
13.It is hard to imagine how Edison managed to work twenty hours each day.
14.There is no doubt that you will be helped by others if you have any difficulties.
15.It is said that bats have been using radar for millions of years.
16.To tell the truth, many mistakes we made could have been avoided.
17.As we know, it was not until recently that the problem was solved.
18.In my opinion, this computer is different from that one you saw.