Frank is working late again. This is the first time this week he's had to study late,_____?   [ ]

A. isn't he      

B. hasn't it    

C. hasn't he      

D. isn't it

已知1g氢气完全燃烧生成水蒸气时放出热量121 kJ，且氧气中1molO=O键完全断裂时吸收热量496 kJ，水蒸气中1 molH-O键形成时放出热量463 kJ，则氢气中1 molH-H键断裂时吸收热量为 [ ]

A．188kJ

B．436kJ

C．557kJ

D．920kJ