Exploring the ocean is difficult. New technology is making the ocean easier to explore.

And or but so

but

Explanation:

exploring the ocean is difficult BUT new technology is making the ocean easier to explore.

the sentence that avoid faulty coordination is:

culture, which is well represented in philadelphia, plays a major role including theatre, music, and the visual arts.  

faulty coordination occurs when the writer gives equal importance two different ideas (clauses) which in fact are not equivalent. in order to correct a misplaced clause or idea, the writer can place less important or emphatic ideas in a relative clause as in the previous sentence.