钢材按质量和含碳量各分为哪几种？
参考答案：
①钢材按质量分为普通钢，优质钢，高级优质钢
②钢材按质量分为低碳钢，中碳钢，高碳钢
当怀疑为上颌窦海绵状血管瘤时应进行的检查是（）。
A.鼻旁窦X线拍片
B.鼻旁窦CT
C.上颌窦诊断性穿刺
D.血管造影
E.活检
Directions:
Study the following picture carefully and write an essay entitled "Noise Pollution. "
In the essay you should
(1) show your understanding about the issue,
(2) state your opinions and use facts to support your statement.
