干细胞是一类具有自我更新和分化潜能的细胞。干细胞的增殖特性为缓慢性和（）。
参考答案：自稳性
The plane _______ at 7:00 p.m.,so I have to be at the airport by 6:40 at the latest. [ ]
A. has left
B. is to leave
C. will have left
D. leaves
为保护炉底，（）等温线应远离炉底.
