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. Iron may be one of the most important factors in controlling phytoplankton production in ocean waters that are rich in other nutrients. B. Results from a recent experiment suggest that several factors limiting phytoplankton production in ocean waters have gone unrecognized. C. Although it was not recognized until recently, nutrients are plentiful in areas of the ocean where iron controls phytoplankton production. D. Until recently, the importance of iron was not taken into account in experiments concerning phytoplankton production.