Ethnography Differs from Other Research Methods in Which of the Following

Ethnography differs from other research methods in which of the following ways?

A) it requires the researcher to be in the field for long hours for a relatively long period of time.
B) it can be done quickly and cheaply by sampling a small segment of the population.
C) it is best at controlling the environment and making sure that extraneous variable do not affect the data.
D) it can be done in the library using precollected data.