17. officer, official

officer部隊(duì)的軍官;
official政府官員 eg:an army officer

18. work, job

二者均指工作。work不可數(shù),job可數(shù) eg:a good job

19. couple, pair

couple主要指人或動(dòng)物;
pair多指由兩部分組成的東西 eg:a pair of trousers

20. country, nation, state, land

country側(cè)重指版圖,疆域;
nation指人民,國(guó)民,民族;
state側(cè)重指政府,政體;
land國(guó)土,國(guó)家 eg:The whole nation was sad at the news.