Answer:
d)a psychological construct
Explanation:
According to the chapter, closeness is a psychological construct. The extent to which a partner includes the perspective of the other in his or her self concept. In a study titled "The path to closeness:  A mediational model for  overcoming the risks of  increasing closeness" by Jennifer M. Tomlinson  and Arthur Aron published in 2013. it was also stated that closeness is a psychological construct.