—— 请按键盘 空白键 开始游戏 ——

"Randomized experiments are the gold standard for causal inference, but they are not always feasible."
The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
我是个战士,我是个奋斗者,我是个幸存者。
The great thing about being old is that you don’t have to worry about the future.