11. _________ one has a child will one realize how great one’s parents are.
| A．Until | B．Until not | C．It is not until | D．Not until |
Anyone can borrow books from this library _______ he keeps them clean and returns them in time.
| A．even if | B．unless | C．so that | D．as long as |
So fast _____that it is difficult for us to imagine its speed.
| A．light travel | B．is light travel | C．does light travel | D．travels light |
Just as the tree is the unit of a forest and the book the unit of a library, ______ the molecule is the unit of matter.
| A．as | B．like | C．so | D．thus |
The door opened and in ________.
| A．rushed they | B．the children rushed | C．they rushed | D．did the children rush |
______ nobody was very enthusiastic about it, they decided to cancel the trip.
| A．See that | B．Seeing that | C．So | D．When |