国际多式联运采取单一的费用（）
参考答案：对
Mum，you really need to have a rest！You ________in the kitchen ever since you came back home three hours ago.
A．had worked
B．were working
C．have been working
D．worked
ABO血型系统中，天然抗体的本质一般是
A．IgMB．IgDC．IgCD．IgE
