一个半径为2cm的圆的内接正六边形的面积是( )
A:24cm2
B:63cm2
C:123cm2
D:83cm2
读中国地形略图,完成各题:
They had received no news of him since his ____ (离开) from the island.
食品保鲜膜按材质分为聚乙烯(PE)、聚氯乙烯(PVC)等种类.PE保鲜膜可直接接触食品,PVC保鲜膜则不能直接接触食品,它对人体有潜在危害.下列有关叙述不正确的是( )