研究人员正在不断拓展科学认知的前沿。

Researchers are constantly pushing ___the ___frontiers ___of scientific understanding.

她的作品位于当代艺术表达的前沿。

Her work is at ___the ___frontiers ___of contemporary artistic expression.

这一发现拓展了医学可能性的边界。

This discovery has expanded ___the ___frontiers ___of what is medically possible.