根据<焊接与切割安全》国标（GB9448-1999）的规定，氧气胶管的颜色是（）。
参考答案：蓝色
A defensive stock is best characterized as:（）
A. being heavily influenced by aggregate business activity.
B. generally retaining a large portion of earnings.
C. having low systematic risk.
治疗慢性阻塞性肺疾病外寒里饮证的代表方剂是（）。
A.真武汤
B.麻杏石甘汤
C.三子养亲汤
D.桑白皮汤
E.小青龙汤
