Only when they were put in prison and lost freedom(自由) _________ its importance.

A．they realized                           B．did they realize

C．realized they                           D．had they realized

No sooner _____ they rushed out into the street.

　 A. did they hear the news than 　 B. had they heard the news than

　 C. did they hear the news when 　 D. had they heard the news when

Everyone should visit a lighthouse at least once.
The most important reason for such a visit is to realize how our ancestors (祖先) battled nature with the basic tools they had . They had only basic ways of creating light , and yet they found a way of using this simple technology in isolated (孤零零的) places to save ships from hitting rocks .
Secondly , visiting lighthouses will help us to understand the lives of lighthouse keepers .By their very nature , lighthouses were built on some rocks or cliffs . Thus , the lighthouse keepers often lived lonely lives . To walk around their small home , and imagine the angry storm outside beating against the walls , is to take a step towards understanding the lives they had.
The reasons for a visit to a lighthouse are not all so backward-looking in time . It is true that lighthouses were built in out-of-the –way places . But on a pleasant sunny summer day. This very isolation has a natural beauty that many people will love to experience . Therefore, with the gentle waves touching all round the lighthouse . the visitor is likely to think it is a world preferable to the busy and noisy modern life.
Another reason for considering a visit is that the lighthouses themselves can be very attractive buildings . Mankind could often not be content just to put up a basic structure . but felt the need . even in such an isolated place , to build with an artistic touch . The result is a view for tired eyes to enjoy .
Finally , lighthouses have a romantic attraction , summed up by the image of the oil-skin coated keeper climbing his winding stairs to take care of the light to warn ships and save lives .
【小题1】What is the reason to look back into the past of a lighthouse ?

Only after liberation       to be treated as human beings.

A．did they begin      B．they had begun     C．they did begin      D．had they begun

 No sooner _____ themselves in their seats in the theatre _______ the curtain went up.

       A．they have settled; before                       B．had they settled; than

       C．have they settled; when                        D．they had settled;than