Which best explains why irving sets "the adventure of the mysterious stranger" in a land of “masks and gondolas”?
the setting is symbolic of the idea that a life of quiet study is the ideal pursuit.
the setting is symbolic of the idea that innocence cannot be outgrown.
the setting is symbolic of the idea that ease and affluence are available to all.
the setting is symbolic of the idea that appearances can be deceiving.

The best statement that explains why Irving sets "The Adventure of the Mysterious Stranger" in a land of “masks and gondolas” is:  

The setting is symbolic of the idea that ease and affluence are available to all.

The characters where in Venice to make their education complete. They would have embarked in a tour to meet new people and immerse themselves in different cultures so that their learnings will not be limited to the things they have learned in their classrooms. This tour is a requirement for everyone of high society regardless if they are monied or not.