— He has a sore back.
A:What is he
B:What does he do
C:What's the matter with him
D:What does he look like
匹兹堡成为钢铁工业中心的有利条件是①地形平坦,水能丰富②历史上是人口稠密的地区,有丰富的劳动力资源③自然资源种类多、数量大,地区组合好,工业接近原料、燃料地④利用五大湖和运河,水运条件十分便利