Answer:
The correct answer for: Si quieres ser viajero educado, ________ (2 palabras) investigar los gestos y costumbres del destino. Is: "tienes que"
Step-by-step explanation:
To start I want to clarify something. In our case, the phrase is talking in general form to the reader or the listener, that is why it is written in an informal format. Now, the phrase translates to If you want to be a polite traveler______ research the destiny's gestures and customs. We are missing the "Have to" verb over there and the Spanish version of "have to" in this case is "Tienes que".