0℃时冰的导热系数为（）W/ｍ•K。
A．2.23
B．2.78
C．3.384
D．4.43
参考答案：A
His sister left home in 1998. and _________ since. [ ]
A. had not been heard of
B. has not been heard of
C. had not heard of
D, has not heard of
油气的引爆能量为（）。
A.0.02mJ
B.0.03mJ
C.0.2mJ
D.0.3mJ
