1 . The psychology of most people is positive and healthy despite the challenges brought by the COVID-19 o_______.(根据首字母单词拼写)

2 . In the early 19th century, when an ________(爆发) of cholera hit Europe, millions of people died from the disease. (根据汉语提示单词拼写)

3 . The ________ (爆发)of Covid-19 has meant great changes in our life and work. (根据汉语提示单词拼写)