Which of the following best completes the following sentence,'The ______ is not the defining element of social publishing;rather,it is the sharing of knowledge via ______ in an environment that also enables discourse and other forms of participation.'?

A) Reach,engagement.
B) Engagement,reach.
C) Content,vehicles.
D) Vehicle,content.
E) None of these.

The sentence suggests that the defining element of social publishing is not the medium or platform used to share content but rather the act of sharing knowledge. Therefore, the first blank must refer to the medium or platform used (i.e., vehicle) and the second blank must refer to the act of sharing (i.e., content). Among the choices, only D correctly pairs vehicle with content.