When Researchers Visited 32 Pubs in One City to Study

When researchers visited 32 pubs in one city to study drinking habits,they recorded their observations on napkins and pieces of newspaper.The reason they kept records in this way was

A) to conduct a double-blind study in each of the pubs.
B) to make sure the study had reliability.
C) to be able to determine experimenter effects at a later point in time.
D) to make sure that their intentions were not obvious to those they were observing.