简述愈伤组织的概念。
参考答案：
是从外植物体的离体材料组织增生的细胞产生的一团不定型的疏散排列的薄壁细胞，是分化的，而且还未形成组织的结构。
已知自由落体运动的速率v=gt，则落体运动从t=0到t=t0所走的路程为______．
Speaker A. The lights are about off, but I'd like to buy some ice-cream before the play starts.Speaker B: ______
A．Which ice-cream would you like, vanilla or chocolate
B．Yes, the lights will be off in five minutes.
C．Shall we take our seats now We can always get some later.
D．May I have the honor to buy it for you
