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5 10 15 20	Tools and hand bones excavated from the Swartkrans cave complex in South Africa  suggest that a close relative of early humans known as Australopithecus robustus may  have made and used primitive tools long before the species became extinct 1 million years ago. It may even have made and used primitive tools long before humanity's direct ancestor, Homo habilis, or "handy man," began doing so. Homo habilis and its  successor, Homo eretus, coexisted with Australopithecus robustus on plains of  South Africa for more than a million years.      The Swartkrans cave in South Africa has been under excavation since the 1940's.  The earliest fossil-containing layers of sedimentary rock in the cave date from about 1.9 million years ago and contain extensive remains of animals, primitive tools, and  two or more species of apelike hominids. The key recent discovery involved bones  from the hand of Australopithecus robustus, the first time such bones have been found.      The most important feature of the Australopithecus robustus hand was the pollical  distal thumb tip, the last bone in the thumb. The bone had an attachment point for a "uniquely human" muscle, the flexor pollicis longus, that had previously been found  only in more recent ancestors. That muscle gave Australopithecus robustus an opposable  thumb, a feature that would allow them to grip objects, including tools. The researchers  also found primitive bone and stone implements, especially digging tools, in the same  layers of sediments.      Australopithecus robustus were more heavily built ― more "robust" in anthropological terms ― than their successors. They had broad faces, heavy jaws, and massive crushing  and grinding teeth that were used for eating hard fruits, seeds, and fibrous underground  plant parts. They walked upright, which would have allowed them to carry and use tools.  Most experts had previously believed that Home habilis were able to supplant Australopithecus robustus because the former's ability to use tools gave them an innate  superiority. The discovery that Australopithecus robustus also used tools means that  researchers will have to seek other explanations for their extinction. Perhaps their  reliance on naturally occurring plants led to their downfall as the climate became drier  and cooler, or perhaps Homo habilis, with their bigger brains, were simply able to make more sophisticated tools.
16. It can be inferred from the first paragraph that all of the following may have made and used tools EXCEPT (A) Australopithecus robustus (B) Home erectus (C) Home habilis (D) Australopithecus robustus' ancestors 17. Which of the following does the author mention as the most important recent discovery made in the Swartkrans cave? (A) Tools (B) Teeth (C) Plant fossils (D) Hand bones 18. What does the third paragraph mainly discuss? (A) Features of Australopithecus robustus' hand (B) Purposes for which hominids used tools (C) Methods used to determine the age of fossils (D) Significant plant fossils found in layers of sediment 19. It can be inferred from the description in the last paragraph that Australopithecus robustus was so named because of the species' (A) ancestors (B) thumb (C) build (D) diet 20. The word "supplant" in line 24 is closest in meaning to (A) exploit (B) displace (C) understand (D) imitate 21. The word "them" in line 25 refers to (A) tools (B) Homo habilis (C) Australopithecus robustus (D) experts 22. The word "innate" in line 25 is closest in meaning to (A) inherent (B) incidental (C) objective (D) irrelevant 23. What does the author suggest is unclear about Australopithecus robustus? (A) whether they used tools (B) what they most likely ate (C) whether they are closely related to humans (D) why they became extinct
16. D 17. D 18. A 19. C 20. B 21. B 22. A 23. D