别在公共场合大声喧哗Do not make loud noises in public.1别在上课时说话 Do not talk during the lessons.2我们不能上课迟到 We cannot be late coming to class.We should come to class on time.3别在街上踢足球Do not play soccer on the street. 4别在教室里玩篮球 Do not play basketball in the classroom.5别撒谎Do not lie. 6你不能太晚睡觉 You should go to sleep earlier.7她不能唱歌,因为她太害羞She is too shy to performance her singing in the public. 8他不能来上课,因为他生病了 He cannot come to school because he is sick.9我不能完成家庭作业,因为我头疼。I cannot (I am unable to) finish my homework on time because I have a headache.
在公共场合大声喧哗Don't shout and cry in public places. Don't makes loud noises in public places. Don't make such a racket in public places. Don't attempt to draw attention to yourself in public places.
同学,我们不应该大声喧哗,要看具体的语境。首先如果表示一种规则的,不准做什么事情,可以用shall. We shall not speak/talk loudly. 一般情况下(不是上面规定的)可以用should来代替shall. 其次,如果这事情已经发生,表示说话人带责备的情绪,可以用We should not have spoken(talked)loudly. 虚拟语气