Tomorrow is Dragon Boat Day. My mother and my grandma _________ a big meal for our family now.
A:are preparing
B:be preparing
C:prepare
D:prepared
关于卢瑟福提出的原子结构的行星模型,下列说法错误的是( )
小红去邮寄物品,邮费分别是1.8元和12.9元,共需____元。