- Is Jack in the next room?
- Well, it's hard to say. But I heard him ________ loudly when I passed by just now.
A:speak
B:to speak
C:spoken
D:speaking
—She's my friend, Yang Ling.
已知-2是方程x2+2x+k=0的一个根,则k的值是____
中国古代农耕方式演变的趋势是( )