已知函数$y=\tan \omega x$在$\left(-\frac{\pi }{2},\frac{\pi }{2}\right)$内是减函数，则$\omega$   （   ）

经过5个多月的市民投票和专家评审，市民文化节组织评选的100个乡土文化符号近日出炉。

       在上海这样一个大都市，乡土文化符号不仅仅指向农村文化，而应把城市化进程中所产生的重要文化符号也纳入进来。“乡土”即“本乡本土”，强调地方色彩和区域文化，物质文化和非物质文化符号均可纳入。

       评选出来的100个乡土文化符号分为名胜史迹、景观地标、海派人文三个类别。其中，名胜史迹作为城市历史记忆的活化石，在入选的100个乡土文化符号中占比逾40%。海派人文类文化符号则囊括了文化名人、海派技艺、民俗风情、特产美食等不同子类别。

根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

    Bruce shook his money box again.

    Nothing! He carefully counted the coins that lay on the bed. All that he had was $24.52. The 1 which he wanted was at least $ 90. How on earth(究竟) was he going to get the rest of the 2?

    He knew that his friends all had bicycles. It was hard to hang out(闲逛) with people when you were the only one 3 a bicycle. He thought about 4 he could do. He couldn't get money from his parents, because he knew they had no extra(额外的) money.

    There was only one way to get money, and that was to earn(挣钱) it. He would have to find a job. He decided to ask Mr. Clay for 5.

    "Well, you can start right here," said Mr. Clay. "You see, my windows need cleaning and my car need washing."

     That was the beginning of Bruce's part time(兼职) job. For the next three 6 he worked every day after finishing his homework. He took dogs for walks and cleaned rooms.

     The day finally came when Bruce 7 his money and found $ 94.32. He wasted no time and went down to the shop to 8 the bicycle he wanted. He rode home proudly, looking forward to 9 his new bicycle to his friends. Bruce liked his bicycle very much because he had bought it with his own money. At last, his dream came true, and his parents were 10 of him.

已知二次函数y=ax²+bx+c（a≠0）的图象如图所示，有下列结论：
①b²﹣4ac＞0；
②abc＞0；
③8a+c＞0；
④9a+3b+c＜0
其中，正确结论的个数是（　　）