Whether to compete or to cooperate has become a hot issue in today's society, both in public and private.

a 是不定冠词，表示"一个"或"某类"。 hot 的本义是"热的"，引申为"激烈的"或"热门的"。 issue 的意思是"问题"或"议题"。 hot issue 指引起广泛讨论和争议的热门话题。