自然群落演替(succession)。
参考答案:
生态系统内的生物群落随时间的推移,一些物种消失,另一些物种侵入,群落组成及其环境向一定方向产生有顺序的发展变化,称为群落演替。
根据句意及首字母提示填空。
1. There is a lot of food and fruits in the r____.
2. I want to book a standard room with two s____ beds.
3. Hello, Wei Hua! Did you receive a p____? I wrote something on it and I sent it to you yesterday.
4. In A____, most people have light skin, but in Africa, lots of people have dark skin.
5. There are four g____ in our school. It's their duty to keep the school safe.
节俭是传统美德。经济学家凯恩斯则提出了节俭悖论,认为节俭对个人、家庭来说是美德,而对社会来说则意味着支出减少,导致有效需求不足阻碍经济发展,造成失业增加,收人减少。这启示我们( )
①既要勤俭节约,又要适度消费 ②应重视消费对生产的影响,积极引导消费
③个人应该坚持节俭,社会应该扩大消费 ④消费决定生产,政府应适当刺激消费
A.①②
B.②③
C.③④
D.①④