如图所示是一列机械波从一种介质进入另一种介质中发生的现象,已知波在介质Ⅰ中的波速为v1,波在介质Ⅱ中的波速为v2,则v1∶v2为( )
A:1∶
B: ∶1
C: ∶
D: ∶
胚是新植物的幼体,由胚芽、胚轴、胚乳和子叶组成.(判断对错)
下列有关人类基因的描述中,错误的是( )
She had to sell the house even though it was _______ her own wishes.