What phrase would you use to thank someone in a formal situation in Korea?

The phrase "Gamsa Hapnida" is the correct choice for expressing gratitude in a formal situation in Korea. This phrase is a polite and formal way to say "thank you" and is commonly used in various contexts, particularly when addressing someone of higher status or in professional settings. Its respectful tone makes it suitable for formal interactions, helping to convey appreciation while maintaining the appropriate level of politeness.

In contrast, the other options do not serve as formal expressions of thanks. Some of these phrases may convey greetings or could be used in different contexts that do not align with the act of thankfulness. Understanding the nuances of formality in language is key in Korean culture, as respect and hierarchy greatly influence communication.