Sentence Correction

Hey Guys

Here is the question,

Just like the background in art history needed by an archaeologist in order to evaluate finds of ancient art, the nautical archaeologist needs specialized knowledge of the history and theory of ship design in order to understand shipwrecks.

"¢Just like the background in art history needed by an archaeologist in order to evaluate finds of ancient art, the
"¢Just as an archaeologist who needs a backgrounds in art history to evaluate finds of ancient art, a
"¢Just as an archaeologist needs a backgrounds in art history to evaluate finds of ancient art, so a
"¢Like the archaeologist who evaluate finds of ancient art and requires a backgrounds in art history, so the
"¢As evaluating find of ancient are requires an archaeologist who has a background in art history, so the

I can't understand why the second sentence can start by ''so a''

Any suggestions?
Many thanks
Lukas