When we talk about the cities in United States the first comes into our mind is New York.

问题补充：

When we talk about the cities in United States, the first comes into our mind is New York.

A. one

B. city

C. that

D. which

答案：

A. one

B. city

(答案→)C. that

D. which

解析：句意:当我们谈论美国的城市，第一个进入我们脑海的是纽约。这里是定语从句，先行词是the first省略了（city）后面是定语从句，在定语从句中缺少主语，用关系代词that，因为是序数词，所以不能用which，也不能省略，所以AB都不对，选C。