如图:△ABC的周长为30cm,把△ABC的边AC对折,使顶点C和点A重合,折痕交BC边于点D,交AC边与点E,连接AD,若AE=4cm,则△ABD的周长是( )
A:22cm
B:20 cm
C:18cm
D:15cm
— Did you hear the news about the fire in our building?
— Yes. It took the firemen two hours to_______ the fire.
分子、原子、离子都是构成物质的微粒,下列物质由阴、阳离子构成的是( )