用括号内所给动词的正确形式完成短文。

    How to Observe the United States

    What is the best way to observe the United States? The best way 1    (depend) on how much you want to spend, what part of the country you want  2        (visit),  what you want to see along the way, and how much time you  3  (have). Sometimes a combination(联合) 4       (be) the best.    5    (fly)is the fastest and possibly the least expensive way to see America. If you   6   (have)a round trip ticket to the United States, many airline companies have special tickets that let you  7     (fly) at a big discount(折扣价).  Although air travel is the fastest, it doesn't allow you    8   (see) very much except clouds when you are traveling. If you want'to see the country from the ground, you should consider    9     (take)a bus.  For short trips around a city or to a national park,  a rental car    10   (be)a good idea,

1._________2._________3._________4._________5._________

6._________7._________8._________9._________10._________

水和油含量各为50%的食品其乳化液有油悬浮在水中和水悬浮在油中两种情况，在外界条件相同时（）冻结速率较快。

A.前者

B.后者

C.一样

D.不确定