在20世纪50年代，太空旅行还处于萌芽阶段。

In the 1950s, space travel was ___in ___its ___infancy.

人工智能在21世纪初仍处于起步阶段。

Artificial intelligence was still ___in ___its ___infancy in the early 21st century.

可再生能源领域在许多发展中国家目前正处于初期发展阶段。

The field of renewable energy is currently ___in ___its ___infancy in many developing countries.