氮的氧化物（NOx）是大气污染物之一，工业上在一定温度和催化剂条件下用NH3将NOx还原生成N2，某同学在实验室中对NH3与NOx反应进行了探究．回答下列问题：氨气的制备
They were smoking the teacher appeared in front of them.
Amy and Sam like _____.
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确表示高等动物胚胎发育顺序的是（ ）