高耸的山脉构成了山谷令人叹为观止的背景。

The towering mountains ___form a breathtaking backdrop to the valley.

她广泛的研究构成了这一突破性理论的基础。

Her extensive research ___forms the foundation of this groundbreaking theory.

在寒冷的晨间空气中，露水在蜘蛛网上形成了复杂的图案。

In the cold morning air, dew had ___formed intricate patterns on the spider's web.