Final answer:
The correct word to fill in the blank is 'visit,' as it fittingly describes the Americans' experience in Vietnam.
Step-by-step explanation:
The correct answer to the question is: 'The foods available in Hanoi restaurants include not only native Vietnamese dishes but also Chinese, French, and American choices among others, which came as a complete surprise to the Americans making their first visit to Vietnam.'
The word visit is appropriate in this context because it implies coming to a place or attending a location for a purpose without denoting the length of the stay or implying an extended and in-depth exploration.