他最近的表现让人对他的领导能力产生了怀疑。

His recent performance has cast ___doubt on his leadership skills.

毫无疑问，定期锻炼能改善健康。

There is no ___doubt that regular exercise improves health.

如果您对这些说明有任何疑问，请尽管提问。

Please ask if you have any ___doubt about the instructions.