__________叫做这种燃料的热值.热值的单位是_______，符号是_______。
1千克某种燃料完全燃烧放出的热量，焦每千克， J/kg
The reporter _____ that the girl who was so _____ was trying not to answer the question. [ ]
A. recognized; frightening
B. realized; frightened
C. recognized; frightened
D. realized; frightening
航天器的返回过程是怎样的？怎样才能确保返回的安全与平稳？
