Answer :
Among the choices, letter B is the most complex. This is because it uses two clauses just to deliver its meaning. Jamming a lot of clauses in one sentence would cause the reader to be 'breathless'. A good sentence must be short enough to be read in one breath, but precise in meaning. One clause could be enough. If you want to add more information, you can use conjunctions or transition words. But do not overdo it.