What does the underlined word “upside” in paragraph 6 mean?

(单选题)In early 2020, most of the teachers in China had to teach at (单选题)To speed up the ______ of letters, the Post Office introduce (单选题)The best title for the passage may be ______. (单选题)To achieve the desired result, humorous stories should be de (单选题)It can be inferred from the passage that public services ___ (单选题)The joke about doctors implies that, in the eyes of nurses, (单选题)To make your humor work, you should ______. (单选题)We can infer from the passage that ______. (单选题)Which of the following about the boy is WRONG? (单选题)When the boy finally told his father that all the nails were