VOA慢速英语:新冠疫苗启动大规模临床试验 美国卫生专家出席参议院听证会

cautiously –adv. careful about avoiding danger or risk

optimistic –adj. having or showing hope for the future: expecting good things to happen

standard –n. a level of quality, achievement, etc., that is considered acceptable or desirable

cutting corners –idiom to save money or time by not following the correct procedures or rules for doing something