——Kitty, do you know ______?——Sure, about forty minutes.
A：when did their class meeting begin
B：where their class meeting was held
C：how often their class meeting is held
D：how long their class meeting will last
①社会实践是文化创新的源泉
②文化创新促进民族文化繁荣
③文化发展的实质是文化创新
④社会实践是文化创新的动力
It's very important _______ us ______ every day.
在物理学中能量的单位是（ ）
