列车车体的防火要求严格，故多采用（）的材料。
A.无毒
B.防火阻燃
C.低烟低毒
D.防火阻燃、低烟低毒
参考答案：D
Elbert Einstein, for ______ life had once been very hard, was successful later in science .
A．whom
B．whose
C．which
D．his
急性乳腺炎最常见的致病菌是
A．厌氧菌
B．肺炎球菌
C．溶血性链球菌
D．金黄色葡萄球菌
E．绿脓杆菌
