I think you know the author's real purpose-to describe people with things (who dared to write such an article brazenly at that time). What he expressed was poplars, but what he really praised was the People's Liberation Army for defending the country. Poplar is a "loan" and PLA is a "metaphor". In short, I read this article when I was studying and learned a lot. Later, I used a lot of articles, which was quite acceptable.