3D打印是以数字模型文件为基础,以粉末状金属或塑料等黏合材料为原料,通过逐层打印的方式生产各种形状的产品的技术;3D打印不用模具,无需机械加工,能够降低生产成本,提高劳动生产率。3D打印技术的发明应用表明①观念的存在不通过实践也能转化为现实的存在②观念的存在与现实的存在没有本质的差别③生产实践活动的具体形式是不断发展的④实践是主观与客观的交汇点和联接纽带
______ that no one was ever prepared for it.
I could tell he was surprised from the _____ on his face.
The book seems to have been _____ from various books and articles.
As more and more cars are produced and used, so the _____ from their exhaust-pipes contains an even larger volume of poisonous gas.
He left in such a hurry that I _____ had time to thank him.