Passage V
Rock types can often be differentiated by the rare earth elements (REEs) they contain. Table 1 shows the average concentration of 2 REEs, neodymium and samarium, in 4 igneous rock types (oceanic basalt, continental basalt, andesite, and granite) and also in 3 sedimentary rock types (shale, sandstone, and dolomite).
Figure 1 shows the relative concentration of REEs in various igneous rock types and in sedimentary rocks taken as a group. Relative concentration is calculated using the following formula:
relative concentration of REE in rock type = 
Meteorites, taken as a group, are used to calculate the relative concentration because their composition is distinctly different from any Earth rock.
Figure adapted from S. Ross Taylor and Scott McLennan, “The Evolution of Continental Crust.” ©1996 by Scientific American, Inc.
27. In Figure 1, the plot of relative concentration versus atomic number covers the smallest range of relative concentrations for which of the following rock types?
Your Answer is
Correct Answer is A
Explanation
Looking at figure 1, which line segment has the smallest range of abscissa values covers the smallest range of relative concentration. The smallest range of abscissa is oceanic basalt