填空题 Selected the topic sentence in each group and marked it TS. Then put the supporting sentences of Paragraphs 2, 3, and 4 in order and mark them SSl, SS2, SS3, and so on. Paragraph 2 __ a. Twelve years after Sputnik, the United States caught up by becoming the first nation to land a man on the moon. __ b. The Europeans have joined the competition, vowing to land European astronauts on the moon by 2025 and on Mars by 2035. __ c. The number of nations competing in the "space race" has grown since the early days of space exploration. __ d. China joined the competition in 2003 when it launched Shenzhou 5. __ e. Initially, the former Soviet Union took the lead when it sent the first man into Earth orbit in the spaceship Sputnik in 1957. __ f. For almost 50 years, the United States and Russia were the only competitors in the contest to explore space using manned spacecraft