先阅读短文，然后根据题目要求及所给语境完成下列任务。

   If you want to have a wonderful vacation, you can visit Kingston(金斯顿 ). It's a famous Canadian city on the bank of Lake Ontario (安大略湖). It is about three hours'  trip by bus from Kingston to Toronto(多伦多 ). There are some famous universities(大学)in Kingston. About 25,000 students study in these universities. Queen's University, founded in 1841, is more famous than any other university in Kingston. Kingston is one of the friendliest cities in the world and it welcomes tourists from all over the world. Wherever tourists go in this city, they will see a warm smile on the street or hear a happy "hello" in a public park. It's easy for them to feel at home

根据短文内容完成表格，每空一词。

3乘5，再加2得18.

①ax²+bx+c=0；②3（x﹣9）²﹣（x+1）²=1；③x+3= $\frac{1}{x}$ ；④（a²+1）x²﹣a=0；⑤ $\sqrt{x+1}$ =x﹣1，

其中一元二次方程的个数是（   ）