Let's ________ closer. ( )
A:swim
B:swims
C:swimming
表1 浸出液成分
Al3+
Fe3+
Ca2+
PO43-
Mg2+
Mn2+
Y3+
浓度/(mg•L-1)
7670
9460
550
640
5600
1500
70.2
集满二氧化碳气体的集气瓶要用____盖好,瓶口向____放在桌上备用.