物流学科研究的对象是（）
A.物流要素
B.物流技术
C.物流系统
D.物流设备
参考答案：C
The building _____ roof is special is a hospital.[ ]
A. which
B. who
C. at which
D. whose
以善于种茶闻名的民族是哪个民族？
e building _____ roof is special is a hospital.[ ]