题目

—did your uncle leave his hometown? — He for nearly twenty years. A . When; has left B . When; has been away C . How long; has left D . How long; has been away 答案：B（6分）（2012?重庆）肼（H2N﹣NH2）是一种高能燃料，有关化学反应的能量变化如图所示，已知断裂1mol化学键所需的能量（kJ）：N≡N为942、O=O为500、N﹣N为154，则断裂1molN﹣H键所需的能量（kJ）是（ ）A.194 B.391 C.516 D.658