1021094
| Question | Answer |
| 1. The causes of gamma-ray bursts throughout the universe, and how the gamma rays are actually produced, ________ until recently remained a mystery. A. have B. have been C. has been D. has | A. have |
| 2. That the legal drinking age ________ lowered is a hot topic for debate in many states. A. should have B. which should C. should be D. should | C. should be |
| 3. Discovery of these ancient anthropic markings ________ our understanding of how these early humans interacted with their environment. A. has broadened B. have broadened C. broaden D. will have broadened | A. has broadened |
| 4. The rivalry between the two communities stems from ancient times and openly __________ to this day. A. persist B. which persist C. persists D. which persists | C. persists |
| 5. Despite the simplicity of their construction, the ancient systems ________ exhibit very complicated behavior. A. find to B. found to C. are found to D. were found to | D. were found to |
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