乳汁中富含抗体，初乳中含量最高的抗体是（）
A.IgM
B.IgG
C.IgD
D.IgE
E.IgA
参考答案：E
A．波速、频率和波长均不变
B．波速不变，频率和波长均发生变化
C．频率不变，波速和波长均发生变化
D．波速、频率和波长均发生变化
The National Park, _____ with cherry tree flowers, looks as though it is covered with pink snow. [ ]
A. covering
B. covered
C. being covered
D. having covered
