色多多在线观看播放-色多多在线观看高清免费-色多多在线观看视频-色多多在线看-欧美aaaaa性bbbbb小妇-欧美aaaav免费大片

The world is a place of chaos and confusion, and the only way to make sense of it is to find your own path through it.

Understanding the universe requires not just intelligence, but imagination.

We teach a subject not to produce little living libraries on that subject, but rather to get a student to think mathematically for himself.

生活要么是一次大膽的冒險，要么什么都不是。