Which of the following correctly describes the election of 1912? The Democrats achieved effective national power for the first time in over...

The correct answer here is 5 -- All of the
above.

I wonder if your textbook is Tindall and Shi's
America: A Narrative History.  If so, you can find all of these
effects of the 1912 election laid out in order at the end of the subsection devoted to
that election (in the edition I have, it's called "The Election of 1912" and is in Ch.
24).

The election was the first time that Democrats had
control of the presidency and both houses of Congress since the Civil War (except for a
brief time in 1893-5 that Tindall and Shi say didn't really
count).

Wilson was a Southerner.  So were 5 of his 10
cabinet members.  This put the South back in power for the first time in a long
time.

The election split the Republican Party.  The
progressive Republicans went with Theodore Roosevelt and the Bull Moose Party.  The more
conservative people stuck with Taft.

Finally, the major
debate of the election was between Wilson's "New Freedom" and TR's "New
Nationalism."

So -- all of those answers are right and
therefore it is all of the above.