Why Do Tax Practitioners Use a Commercial Tax Service When

Why do tax practitioners use a commercial tax service when most primary sources are available for free on the Internet?

A) Commercial tax services provide editorial explanations and expert analysis of primary tax law.
B) Practitioners are able to provide faster, more accurate solutions to clients' tax problems.
C) Tax services facilitate more efficient, effective, and comprehensive searches.
D) Commercial tax services organize tax law source materials into a single database system.
E) All of the above