the public sector中的public是形容词，用于修饰后面的名词 sector，意思是：公共部门。

又如下面句子，public 也是形容词，修饰后面的名词。如：

We are going to conduct a public opinion poll. 我们将进行民意测验。

I hope my ideas are in step with public opinion. 我希望我的想法与公众舆论是一致的。

The Government is determined to check the growth of public spending. 政府立意控制公共开支的增长。

The disclosure that he had been in prison ruined his chances for public office. 他曾经坐过牢一事的泄露毁了他任公职的机会。

 但是，下面句子中的 public 是名词（the public 意思是“公众”）。如：

The museum is open to the public. 这家博物馆是对公众开放的。

He’s brought this fact to the attention of the public. 他已使公众注意到这一事实。

Police warned the public to be on the alert for suspected terrorists. 警方警告群众警惕涉嫌的恐怖分子。