36. John F. Kennedy was sworn in as the 35th president of the United States ________.

(A) in his forty
(B)on his forty
(C)in his forties 
(D)on his forties

36. John F. Kennedy was sworn in as the 35th president of the United States ________.
(A) in his forty 
(B)on his forty 
(C)in his forties  
(D)on his forties

實際上沒錯的話這是30s 或40s 翻成英文而來的,原本是30 years,和40 years。例如1930s 或是1830s。在說在1930~1939這段期間。這原句是 the decade of 1930 years 或是 the decade of 1830 years的縮寫。

這是算西元的歲數。後來就所有人就很習慣的就把the decade of 省略了和 years就變成 1930s

就這樣形成了 習慣用法零結尾的年+s 就是表 那年的十年。0~9 年共十年。

所以這是說期間的意思。因為是算一個人一生的年代(period)不是算西元的年代(期間)所以你要加所有格his你不是西元

decade=期間十年。所以in his forties = in the decade of his 40s

因此這意思是說在某段期間而要表示"在某段期間時內的事"我們要用 in 來表式。

不能用on是因為沒有前後文可以證明這期間對john是特殊日子或時間。

另外

in 的話是表視在期間內(within)或在期間後(after)的意思。

例如說有人和你說東西一星期後會到是in a week.所以是下星期一或星期二才會到如果你星期日或是星期六跑去應該會被白眼吧。剛看字典翻成一周內……實際上慣用都是 一周後才對。不能用後解釋時才會用within解釋。

因此答案 in his forties.

實際上當慣用語記吧…… in his 40s. 因為他不是西元所以要加his.但題目已幫大家加了那就是只剩需選期間的in。

Teenagers 

十幾歲的孩子

in one's teens

十幾歲

in one's thirties

三十幾歲的人

John F. Kennedy was sworn in as the 35th president of the United States in his forties.

John F. Kennedy在他四十幾歲時宣誓就職第35屆美國總統