他是该国生态学领域的领先专家。

He is a ___leading expert on the country's ecology.

这家公司是世界领先的音频设备制造商。

This company is the world's ___leading manufacturer of audio equipment.

确实，努力工作对家庭福利和国民经济都起着主导作用。

Indeed, hard work plays the ___leading role in both family welfare and the national economy.