A Drawback of Using Secondary Sources in Reviews of the Research

A drawback of using secondary sources in reviews of the research literature is that

A) for many topics in education, primary sources are more accessible.
B) changes and omissions may have been made in the description of the original studies.
C) it takes longer to obtain an overview of a topic when using secondary sources.
D) the number of secondary sources in education and the social sciences is very limited.