I was much impressed by the modern life in Hong Kong ______ I came to visit this fantastic city. [ ]

A. at the first time

B. for the first time

C. by the first time

D. the first time

患者，男，67岁。支气管哮喘，护士巡视病房时，发现患者表情痛苦，烦躁不安，呼吸困难加剧，发绀明显，血气分析：氧分压为<4.8kPa，二氧化碳分压>9.8kPa。

根据患者症状及血气分析，判断其缺氧程度为（）。

A.极轻度

B.轻度

C.中度

D.重度

E.过重度