Which of the following activities could disqualify a non-U.S. citizen under INA 212(a)(3)?

Participating in espionage or sabotage is a disqualifying activity outlined under INA 212(a)(3) because it poses a serious threat to national security. The Immigration and Nationality Act specifically addresses offenses that could undermine the safety and sovereignty of the United States. Engaging in actions that involve gathering or transmitting information that could be used against U.S. interests, or deliberately hindering national defense efforts, is viewed as a significant violation that justifies excluding individuals from entry or residency.

On the other hand, having military training outside the U.S. alone does not automatically disqualify someone unless that training relates directly to hostile actions against the U.S. Similarly, volunteering for a charity organization is generally seen as a positive activity and does not imply any malicious intent. Traveling for tourism purposes is also harmless and considered a legitimate reason for non-U.S. citizens to enter the country. Therefore, only the act of participating in espionage or sabotage falls under the critical conditions that can lead to disqualification based on the mentioned statute.