-- I had a pleasant winter vacation with my family in the north.
-- ______.
A:Oh, that's nice of you
B:Enjoy yourself
C:Well done
D:Glad to hear that
如图四幅图片分别表示四冲程内燃机的四个冲程,它们正确的工作循环是( )
唐朝时期的人不可能做到的是( )