下列那一类植物能做监测空气污染程度的指示植物( )
A:蕨类植物
B:藻类植物
C:种子植物
D:苔藓植物
按照句子顺序给图片写序号。
①They'll visit our classroom.
②They'll visit the art room.
③They'll go to the hall.
④They'll go to the library.
⑤They'll meet the teachers in the meeting room.
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一个十二面体共有8个顶点,其中2个顶点处各有6条棱,其它顶点处都有相同的棱,则其它顶点处的棱数为____