Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. The first question to be answered is how Earth's atmospheric carbon dioxide either got dissolved in the oceans or got chemically bound into carbonate rocks. B. The fact that Earth's abundant carbon dioxide is more often found in carbonate rock than dissolved in the oceans is the answer to the first question. C. Earth still has abundant carbon dioxide, but instead of being in the atmosphere it is now dissolved in the oceans or chemically bound into ocean rocks. D. The formation of limestone and marble used up the carbon dioxide that was dissolved in Earth's oceans so that only carbon dioxide in atmospheric form remained.