If the eyes are the romantic's window into the soul, _  In a study published last month in the journal Science, Peter Ungar of the University of Arkansas and his partner, Matt Sponheimer of the University of Colorado, US, examined the teeth of our early human ancestors to find out what they were really eating. They already knew that different foods cause different marks on teeth. Some cause scratches, while others cause pits  .The carbon left on teeth by different foods is also different. Tropical grasses, for example, leave one kind of carbon, but trees leave another kind because they photosynthesized (  ) differently. Traditionally, scientists had looked at the size and shape of teeth and skulls (  ) to figure out what early humans ate. Big flat teeth were taken to be signs that they ate nuts and seeds, while hard and sharp teeth seemed good for cutting meat and leaves. But this was proven wrong. The best example was the Paranthropus  , one of our close cousins, some of which lived in eastern Africa. Scientists used to believe Paranthropus ate nuts and seeds because they had big crests on their skulls, suggesting they had large chewing muscles and big teeth. If this had been true, their teeth should have been covered with pits like the surface of the moon. They would also have had a particular type of carbon on their teeth that typically comes from tree products, such as nuts and seeds. However, when the two scientists studied the Paranthroupus, it turned out to have none of these characteristics. The teeth had a different kind of carbon, and were covered with scratches, not pits. This suggests they probably ate grass, not nuts and fruit stones. It was the exact opposite of what people had expected to find. Carbon "foodprints" give us a completely new and different insight into what different species ate and the different environments they lived in. If a certain species had the kind of carbon on its teeth that came from grasses, it probably lived in a tropical grassland, for example. The example of the Paranthropus was mentioned in the article in order to   _  .
tell readers that they are one of our close cousins living in eastern Africa tell readers they had different eating habits from modern humans prove that size and shape of skulls does not show accurately what early humans ate tell readers that living environment makes a difference to skull structure
Question: If the eyes are the romantic's window into the soul, _  In a study published last month in the journal Science, Peter Ungar of the University of Arkansas and his partner, Matt Sponheimer of the University of Colorado, US, examined the teeth of our early human ancestors to find out what they were really eating. They already knew that different foods cause different marks on teeth. Some cause scratches, while others cause pits  .The carbon left on teeth by different foods is also different. Tropical grasses, for example, leave one kind of carbon, but trees leave another kind because they photosynthesized (  ) differently. Traditionally, scientists had looked at the size and shape of teeth and skulls (  ) to figure out what early humans ate. Big flat teeth were taken to be signs that they ate nuts and seeds, while hard and sharp teeth seemed good for cutting meat and leaves. But this was proven wrong. The best example was the Paranthropus  , one of our close cousins, some of which lived in eastern Africa. Scientists used to believe Paranthropus ate nuts and seeds because they had big crests on their skulls, suggesting they had large chewing muscles and big teeth. If this had been true, their teeth should have been covered with pits like the surface of the moon. They would also have had a particular type of carbon on their teeth that typically comes from tree products, such as nuts and seeds. However, when the two scientists studied the Paranthroupus, it turned out to have none of these characteristics. The teeth had a different kind of carbon, and were covered with scratches, not pits. This suggests they probably ate grass, not nuts and fruit stones. It was the exact opposite of what people had expected to find. Carbon "foodprints" give us a completely new and different insight into what different species ate and the different environments they lived in. If a certain species had the kind of carbon on its teeth that came from grasses, it probably lived in a tropical grassland, for example. The example of the Paranthropus was mentioned in the article in order to   _  .
A. tell readers that they are one of our close cousins living in eastern Africa
B. tell readers they had different eating habits from modern humans
C. prove that size and shape of skulls does not show accurately what early humans ate
D. tell readers that living environment makes a difference to skull structure
Answer: