During and immediately after a war, Hollywood films typically trumpet the glory of sacrifice and unquestioning patriotism. Ten to fifteen years later, however, morally fraught and sometimes pacifistic movies about the conflict typically emerge. For example, after America joined World War I in 1917, the still infant film industry glorified the fight against "the Hun." But by the early 1930s, films such as All Quiet on the Western Front did not shy away from depicting the horrors of combat and the disillusionment of soldiers. After World War II began, the cycle repeated itself.
Guadalcanal Diary, produced during the second world war, portrayed "the ultimate sacrifice" as a noble and undisputed good while diminishing the ethical complexities. By 1957, though, films such as The Bridge on the River Kwai, first published in book form in 1952, were winning awards for depicting the moral confusion inherent in war.
Subsequently, the movie The Green Berets, produced at the height of the Vietnam war in the late 1960s, was far closer in tone to Guadalcanal Diary than to The Bridge on the River Kwai. A decade or more passed before the film industry finally began producing more complex and ambivalent depictions of the Vietnam war, such as Apocalypse Now and Platoon.
For what purpose does the author include the second sentence of the passage?

文章主题是要讲电影的描述内容随着战争时期与非战争时期反复变化。第一句话说了战争时期电影歌颂牺牲,第二句话说了随后不打仗了电影就开始描绘战争残酷。第三句话就开始举例了。所以前两句组合起来是文章中心论点。不存在B里面的提供了例子支持中心论点,因为第二句话本身就没有例子。选A

