根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

    It is August in Qingdao. It's very 1 here. Now, there are many people 2 vacation. They go to the beach and have 3   good time there. Today is 4, and it is not very hot. On the beach, a lot of people 5 to their friends 6 looking at the beautiful sea. Some of them are 7. Others are taking 8. Can you find 9? I'm the boy in blue shorts. I'm going to surf. It's  10. 

①熟石灰可用来改良土壤酸性 

②氦气可做保护气 

③干冰可作制冷剂 

④蒸馒头时可用NaOH来除去面团中发酵产生的酸

⑤可用Al（OH）₃治疗胃酸过多  

⑥工业上可用Na₂CO₃来制肥皂  

⑦工业上可用铁桶盛放波尔多液 

⑧家庭中可用NaNO₂作调味品．