【单选题】—Are you free after school? —Sorry: I’ve planned to treat a friend of mine to dinner for his help.
【单选题】If you ________ Beijing Duck,I'd like to treat you to a meal at a famous duck restaurant.
【单选题】家禽的肱骨为含气骨,近端有一气孔,与( )气囊相通。
【单选题】家禽的( )为含气骨,近端有一气孔,与锁骨气囊相通。
【单选题】无差异曲线上某一点切线的斜率的绝对值表示( )。
【单选题】家禽的( )为含气骨,近端有一气孔与锁骨间气囊相通。