translation of the following sentences

We are a hospitable city, and our visitors share the joy and fun that is synonymous with the Olympics.
我們是好客的城市,而遊客在此分享的喜悅和樂趣，就是奧運的同義詞．

This is a once-in-a-lifetime event for China and for Hong Kong, as a co-host city.
這對中國和香港－－作為協辦城市來說，是千載難逢的項目．

The horse is considered as much as an athlete as the human rider.
馬匹被視為同騎師一樣的運動員．

…Chinese emperors were pound of owning vigorous horses to show the dynamic power of the dynasty.
古代中國帝王以擁有名駒來炫耀朝代的動力．

Humans have always been addicted to the beauty of horses, the desires for excitement and speed, thus horse racing has ancient roots and Thoroughbred horse racing is the most popular form worldwide.
人類經常折服於馬的美態`刺激的速度，所以賽馬源於古代，名種馬風靡全球．

請解答多兩個問題，為何Olympics前要加the？
專有名詞:例如the sun, the moon,the sea,

once-in-a-lifetime event 前加a 是否正確？
正確
once-in-a-lifetime係自組形容詞，以－串連名詞，形容event, a係指示event嘅冠詞.即係an event(可數名詞)係啱嘅,a xxx event就啱

我們是一個好客的城市，遊客都分享到奧運代表的喜悅和樂趣。
這是中國百年難遇的盛事，對成為協辦城市的香港也是一樣。
馬匹和騎者一樣，都被視為運動員。
中國帝皇昔日都以擁有駿馬為榮，以此彰顯一朝國力。
人們一直都為馬匹的美態、對刺激和速度的渴望著迷，故此賽馬歷史悠久，而其中純種馬的賽事是全球最受歡迎的一種。
（thoroughbred 就係我地日常跑馬見o個ｄ馬）
Olympics 係一個 proper noun，即係名稱之類。有冇用 the，其實係傳統用落係點就係點，冇乜準則。地理名稱一類就多數冇。
once in a life time 四個字，但如果用 hyphen 黐埋，就成為一個形容詞。好似：
a boy 冇問題；a naughty boy 都冇問題。
咁 a naughty five-year-old boy 點會有問題？