A criminologist visits the Library of Congress to analyze letters and political correspondence of Martin Luther King, Jr. This research method is called:

Explanation:

a criminologist secretly studies groups by temporarily deceiving them as to his or her real purpose. hope this helps:)

unless they converted, many non-christians (mainly jews and muslims) were persecuted

intimacy, passion and commitment are the components of a interpersonal relationship emphasized in the triangular theory of love by robert sternberg.

the triangular theory of love says love can be comprehend as this componest form the vertices of a triangle.  

intimacy relates to feelings such as of closeness and connection;

passion relates the drives that brings people together, as physical attraction.

commitment relates to the being in a long-term relationship.