That year I went to the college. On the first day of the term, I was so s小题1: that an old lady sat next to me. She was very old, but she looked very a 小题2:   .

“Why are you in college at such an a 小题3:, Rose?” I asked her. “I’m here to meet a rich husband, get married, have several children and t 小题4:   ,” she answered jokingly. I was interested in what has made her take on this challenge (挑战) at her age. “In fact, I always dreamed of having a college education and now I’m getting o小题5:  .” she told me. Later, we became friends.

At the end of the term, she gave a talk to our class. I’ll never forget what she said. She cleared her throat (嗓子) and b小题6:  , “We do not stop w  小题7:   because we are young; we grow old because we stop. Do you hope to stay young, be happy, and become s小题8:  ? Do you have a dream? I had a dream of going to college. It almost took me all my lifetime, but h小题9:   I am. Never lose your dreams and never give up.” We were all moved by Rose’s words. And I still remember her words in all my life, so I continue my dreams and try my best to a 小题10:  them.

已知定义在实数集R上的函数f（x）=ax³+bx²+cx+d，其中a，b，c，d是实数．

（1）若函数f（x）在区间（-∞，-1）和（3，+∞）上都是增函数，在区间（-1，3）上是减函数，并且f（0）=-7，f′（0）=-18，求函数f（x）的表达式；

（2）若a，b，c满足b²-3ac＜0，求证：函数f（x）是单调函数．