Eshonai wants to understand how people's openness to new experiences and number of countries already visited impacts their willingness to vacation to a country they haven' t been to yet. She also wants to take into account whether they were born in the US or somewhere else. She defines openness to new experiences as, "the extent to which people feel a need for variety, are motivated to experience new things, and critically engage with their experiences." Openness to new experiences is a(n):

1. a. Indirect observable
2. b. Operationalization
3. c. Construct
4. d. Direct observable