焚烧处置技术对环境的最大影响是( )。
A．炉渣污染 B．尾气造成的污染 C．飞灰污染 D．噪声污染
参考答案：B
When the old man ____ to walk back to his house, the sun ____ itself behind the mountain. [ ]
A. started; had already hidden
B. had started; had already hidden
C. had started; was hiding
D. was starting; hid
北京2008年将举办第29届奥运会，北京政府拟建一条磁悬浮铁路，关于这条铁路的性能和现行普通铁路相比在①平稳性好；②噪声小；③阻力小；④运动速度快的说法中正确的是（ ）
A．①②③④
B．①③④
C．①②④
D．②③④
