The scientists at the University of Bern in Switzerland have used a weakened virus that is not
infectious
and has proved safe and effective.
【正确答案】
C
【答案解析】解析：题干：瑞士伯尔尼大学的科学家们利用了一种变弱的病毒，它不具传染性，并已证明是安全有效的。infectious易传染的；contagious传染性的，会感染的；dangerous危险的；harmful有害的；invading入侵的。根据题意，本题选C。