他因试图窥探军事设施而被捕。

He was arrested for attempting to ___spy on military installations.

一些国家担心移民可能为敌对国从事间谍活动。

Some countries fear that immigrants might ___spy for hostile nations.

卧底特工经常窥探犯罪组织以收集情报。

Undercover agents often ___spy on criminal organizations to collect intelligence.