根据短文内容，选择正确答案
B
    We can not live a modern life without travelling. The fastest way of travelling is by air. With a plane one can travel in one day to places which it takes a month or more to get to a hundred years ago. 
    Travelling by train is slower than by plane, but one can see the country while-he is travelling through. Modern trains have comfortable seats and dining-cars. They make even the longest journey enjoyable.
    Some people prefer to travel by sea when possible. There are large luxury liners(客轮) or river boats. They are not as fast as trains or planes, but travelling by sea is a very pleasant way to spend a holiday.
    Many people like to travel by car. They can make their own timetable. They can travel hundreds of miles a day, just as their wish. They can stop wherever they want to see something interesting or to enjoy a good meal at a good restaurant, or to spend the night at a hotel. That is why people choose travelling by car for pleasant trips, while they usually take trains or planes for business.

请谈谈你对文中画线句的深刻含意的理解。

根据课文默写。
①参差荇菜，左右流之。窈窕淑女，                。  （《诗经·关雎》）
②                ，白露未晞。所谓伊人，在水之湄。    （《诗经·蒹葭》）
③                 ，春风不度玉门关。                （王之涣《凉州词》）
④                 ，单于夜遁逃。                   （卢纶《塞下曲》）
⑤                 ，正是河豚欲上时。 （苏轼《惠崇〈春江晚景〉二首（其一》》）
⑥晓战随金鼓，                    。 （李白《塞下曲六首·其一》）
⑦土地平旷，屋舍俨然,                 。(陶渊明《桃花源记》 )
⑧                     ，猿则百叫无绝。（吴均《与朱元思书》）
⑨                      ,处江湖之远则忧其君。（范仲淹《岳阳楼记》
⑩且壮士不死即已，死即举大名耳，                    。（司马迁《陈涉世家》）

二次函数y=ax²+bx+c（a，b，c为常数，且a≠0）中的x与y的部分对应值如下表：

X	﹣1	0	1	3
y	﹣1	3	5	3

下列结论：

⑴ac＜0；

⑵当x＞1时，y的值随x值的增大而减小．

⑶3是方程ax²+（b﹣1）x+c=0的一个根；

⑷当﹣1＜x＜3时，ax²+（b﹣1）x+c＞0．

其中正确的个数为（   ）

如果a²＝ a ，那么a＝____。