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 limited variety in the subjects of rock art paintings has become increasingly evident in the many sites discovered. B. The limited repertoire of subjects found in rock art has made it difficult for archaeologists to determine when each painting was created. C. In the first place, there is little new archaeological information on the subject of rock art because of the limited number of recent discoveries. D. Because many rock art sites cannot be dated, archaeologists have limited information about how rock art varied from period to period.