已知点C是线段AB上的一点，如果线段AC=8cm，线段BC=4cm，则线段AC和BC的中点间的距离为____．

求证：对任何实数k，x²+y²﹣2kx﹣（2k+6）y﹣2k﹣31=0恒过两定点，并求经过该两定点且面积最小的圆E的方程；

阅读下面图表，完成后面题目。

某校学生图书馆阅览室共有十万册图书，再最近一次图书状况调查中，调查人员发现：

请根据图表所反映的情况，写出两条结论：

①一月0℃等温线           ②1600毫米年等降水量线

③季风区与非季风区的界线   ④亚热带与暖温带的界线

根据句意，用括号内所给单词的正确形式填空。（一空一词）

1.They are organizing the____  (thirty-nine) sports meeting of their school.

2.The house____ (it) is very beautiful, but the river near it is much polluted.

3.The boy's dad was ____ (complete ) shocked when he saw that his son was playing with fire.

4.The news and talk shows may not be very exciting, but we can expect ____  (learn) a lot from them.

5.My grandfather's sunny character has a great ____ (influent) on me in my life.