We spend about one-third of our lives sleeping. We know relatively little

A. We shall know more about our sleep if we spend more than one-third of our lives sleeping

B. We know relatively little about our sleep; as a result, we spend about one-third of our lives sleeping

C. Despite spending about one-third of our lives sleeping, we know relatively little about our sleep

D. We spend about one-third of our lives sleeping so that we know relatively little about our sleep