The police chief advised his men to keep________ and not lose their tempers.

依次填入下列各句横线处的词语，最恰当的一组是（ ）①逐步推广使用清洁的可再生能源，减少使用污染环境的能源，是 环境恶化的正确选择。②国庆长假期间，凡在本公司购买商品满1000元者，本公司将 价值100元的礼品券。③作者科尔曼年轻气盛，观点鲜明，但常常论据不足或论证不周，______显得犀利有余，老练不够。④连学好母语都需要花大力气，下苦功夫，_______学习外语呢

The search was________ when night came，even though the child had not been found.

Your mother know the truth, but I am not sure.

On the surface of the water________, which spoiled the beautiful scenery of the park.