研究人员不断探索科学和技术的前沿。

Researchers are constantly exploring ___the ___frontiers ___of science and technology.

这一发现有助于拓展人类知识的边界。

This discovery helps to push back ___the ___frontiers ___of human knowledge.

太空探索考验着人类能力和工程的极限。

Space exploration tests ___the ___frontiers ___of human capability and engineering.