这四种化合物具有下列转化关系(部分反应物、产物及反应条件已略去).
请回答:
“其制两柄上弯,高可三尺……其所盛种粒,各下通足窍,仍旁挟两辕,可容一牛,用一人牵,傍一人执耧,且行且摇,种乃自下。”这段话描述的农具出现于( )
①铜元素____
②4个二氧化硫分子____
③氮气____
④7个亚铁离子____
⑤3个硫酸根离子____
⑥碳酸根离子____
⑦氦气____.
— How many students will join in the sports meeting next week?
—About two hundred. They are all excellent athletes.