68. A 考查细节理解。由第一段第三句"Unlike real inland seas, which seem strangely still, the Atlantic is rich in oceanic liveliness."可知，大西洋总是精力充沛的。

69. C 考查推理判断。由第一段最后一句"It is perhaps not surprising that its vitality has been much written about by ancient poets."可知，作者在文中引用这首诗歌正是为了举例说明大西洋的生机与活力。

70. A 考查词义猜测。由画线词所在句中的"unimaginable quantities of creatures, little and large alike, mix within its depths in a kind of oceanic harmony"可知，A项正确。

71. B 考查推理判断。由最后一段最后一句"It has personalities: sometimes peaceful and pleasant."可知，作者把大西洋比作具有个性的人，所以B正确。