also, the question is about ratio not 直线的斜率.

来源: 于 2012-08-10 08:56:46 [旧帖] [给我悄悄话] 本文已被阅读：次

for my No 1 son, he followed the class and I didn't pay any attension for his study. my No 2 son, school insisted he has to skip a grade. I want to make sure he knows all the topics that the grade covered.