The first case of COVID-19 was reported on December 1st, 2019, (46) the cause was a then-new coronavirus later named SARS-CoV-2. SARS-CoV-2 may have originated in an animal and changed (mutated) so it could (47).. illness in humans. In the past, several infectious disease outbreaks have been traced to viruses (48). originated in birds, pigs, bats and other animals that mutated to become dangerous to humans. More infections can result in more people getting very sick and also create more (49) for the virus to develop further mutations. Research continues, and (50).. study may reveal how and why the coronavirus evolved to cause pandemic disease. 46. A. and B. but C. or D. so 47. A. create B. make C. cause D. lead 48. A. who B. which C. what D. whose 49. A. development B. improvement C. opportunities D. advantages 50. A. much B. many C. most D. more