可持续发展不是选择,而是煤炭行业的必然要求。
自然界的存在与任何命题的存在是同一类型的事实。
Every mathematical problem is a puzzle waiting to be solved, and every solution is a step towards greater understanding.
如果你想在数学上取得进步,你必须习惯于不舒服。
I believe that one can write a great opera with real characters, real emotions, and real situations.