Na₂CO₃俗称纯碱，是一种白色粉末，可以跟CO₂和H₂O反席牛成NaHCO₃，该反应的化学方程式 ____；Na₂CO₃与稀盐酸反应放出CO₂，但实验室却不用这个反应制备CO₂，其主要原因可能是 ____。已知Na₂CO₃的溶解度比NaHCO₃大，那么在饱和的Na₂CO₃溶液中持续通人CO₂，可观察到的现象是____。

人属于生态系统中的什么成份

阅读下面材料,在空白处填入适当的内容(1个单词)或括号内单词的正确形式.

    In London, there are many so-called pop-up shops(流动商店). Why they get such a name is that they are just temporary ____ (arrange).

    Pop-up shops first appeared in the UK in the early 2000s. They were____ (origin)a way for small companies to rent small space in great locations.

    In 2008，many businesses had to shut down. Shops and some offices____ (leave)empty when people stopped____ (run) them. Smart businessmen occupied some of them quickly because they could start a business with much ____ (low) risk. The temporary nature of a pop一up gave them the opportunity____ ( test) a product and develop a customer base. Being small made ____ easier for pop-ups to expand if they were successful.

    Pop-up shops can take many different forms. They might be temporary shops in the high street or a shopping centre. hey might be simple market stalls. According to a 2014 report made ____the Centre of Economic and Business Research, the pop-up industry was worth £2. 1 billion ____ it is expected to grow by 8.4% this year.

    Almost anything____ can be on a high street can also be a pop-up. In an age of fast changing habits, the pop-up idea might be here to stay.