When you can't hear clearly. What should you say? __________
A:I don't know the word in English.
B:Where have you been?
C:I beg your pardon.
上述材料要求我们重视怎样的史学方法?反对哪两种错误史观?在研究人类起源问题上,我们尤其要重视什么样的证据?
化学键
P﹣P
P﹣O
O=O
P=O
键能/kJ•mol﹣1
197
360
499
X
已知白磷的燃烧热为2378.0kJ/mol,白磷完全燃烧的产物结构如图所示,则上表中X=kJ•mol﹣1.( )