Why Is Direct Observation Rarely Used to Collect Social Network

Multiple Choice

Why is direct observation rarely used to collect social network data? Direct observation

A) used to be preferred,as in ethnographies of small societies,but it is less feasible with large populations.
B) does not reveal people's motivations or tie valences,and thus it does not produce useful data.
C) has been replaced by "big data" generated from people's digital lives.
D) cannot be reduced to matrix-based data organization.