Which statement BEST explains the main argument presented in paragraph 4 of The Importance of Sending People to Space? A The history of space exploration demands that humans continue to explore, regardless of the cost. B Continuing to send robots into space in place of humans will ultimately result in limited knowledge. C Sending human beings into space may be three times more expensive than sending robots, so it may not be worthwhile. D The cost of human space exploration may seem like it costs more, but it could be worth the expense.