Once Collection of Data in a Research Project Begins, There

Once collection of data in a research project begins, there can be many problems with collection. A very common problem in the international arena is nonresponse
Due to:

A) a reluctance to be photographed.
B) a reluctance to talking with strangers.
C) a reluctance to talking with officials or official pollsters.
D) a fear of government reprisals.
E) a fear of cultural conflict.