When we practice_____English,we often end up___in Chinese.
A:speaking,speaking
B:speaking, to speak
C:to speak,speaking
D:To speak, to speak
某军事试验场正在平地上试射地对空导弹,若某次竖直向上发射导弹时发生故障,造成导弹的v﹣t图像如图所示,则下述说法中正确的是( )
Fe2+ ⇌④① Fe3+ ⇌③② FeO42﹣(高铁酸根离子)
请回答下列有关问题: