7 years ago they were talk about building another apartment complex in the park.

talk 是动词，意思是"谈话、讨论"，这里用的是过去进行时 talking。 about 是介词，表示"关于、有关"，用来引出讨论的具体内容。 talking about 是一个常用短语，意思是"谈论、讨论"，后面接讨论的具体话题或内容。