题目

 — Why were you not at the concert last night?   — I ______ a close game between Seattle Sonnies and Miami Bucks.  A. watched            B. was watching  C. have watched        D. had watched 答案：B 解析: 本题考查时态。过去进行时表示过去某段时间正在进行的动作。 在内燃机工作过程中，由如图所示的内燃机能流图可知，它的能量损失所占的百分比是：废气内能35％，散热损失30％，机械损失10％，则内燃机的热机效率是________．在高效利用能源同时，必须重视保护环境．