Technological innovation is the fundamental way to solve the problems of the coal industry.

He strolled like a man in the park without a care or a worry in the world. Like he had>

Mathematics teaches us to think logically and creatively at the same time.

试管婴儿的研究是出于帮助不孕夫妇的愿望。

随机实验是因果推理的黄金标准，但它们并不总是可行的。