铝青铜、黄铜的结晶温度范围很小，具有壳状凝固特性，流动性较好，但容易形成集中缩孔，必须设置较大的冒口，充分（）
A.冷却
B.补缩
C.氧化
参考答案：B
—The rain came to a stop the night before. The fields are still full of water.
—It _____ for nearly a week. [ ]
A. had rained
B. has rained
C. would rain
D. was raining
（）的快轮制陶技术和渗碳技术工艺发达，蛋壳黑陶制作工艺空前绝后。
A.中原文化区
B.甘青文化区
C.长江中游文化区
