What is one suggestion for effective interaction? never ask questions of the other person. avoid topics that cause disagreement. use an appropriate level of formality.

A suggestion for effective interaction is to use an appropriate level of formality.

Explanation:

In human interaction, we have to adequate our behavior to the kind of person that we are talking with and in the kind of situation that we are in, all this represents the appropriate level of formality, as we project ourselves to others in our way, we create a fluent communication and both sides become more receptive.

c. with one finger is the answer