下列地基哪些不宜采用人工挖孔桩底灌注桩（）。
A.一般黏性土及填土
B.淤泥及淤泥质土
C.碎土和碎石土
D.季节性冻土和膨胀土
参考答案：B
____ no doubt that the Great Wall is one of the wonders of the world. [ ]
A. There is
B. It is
C. There has
D. It is with
冶炼之后的钨呈( )色。
A．银白
B．红
C．黄
D．黑
