By the time the teacher _______ back, we ________ the thorough cleaning.
A:came, have finished
B:comes, have finished
C:will come, will have come
D:comes, will have finished
通过你的努力,你最终获得了丰富的资料,接下去你应该做的工作( )
某研究者用非洲爪蟾性腺为材料进行了下列实验. 请回答下列问题:
(1)对非洲爪蟾的精巢切片进行显微观察,绘制了如图1示意图.
图1中甲、乙、丙、丁细胞含有同源染色体的有____ ;称为初级精母细胞的有____ .丁细胞中染色体的互换区段内同一位点上的基因____ (填“相同”、“不相同”或“不一定相同”).
(2)如对卵巢切片进行显微观察,无法看到和乙细胞同时期的细胞,其原因是____ .
(3)该研究者进行了一系列“诱导早期卵母细胞成熟的物质”的实验,结果如图2:
由实验一可得出推论:____ 含有可以诱导卵母细胞成熟的物质.
由实验二可得出推论:这种诱导早期卵母细胞成熟的“促成熟因子”的化学成分是____;孕酮在实验二中的作用是____
电脑键盘上的字母为何不按顺序排列?请你来做一项统计,下面是一篇小短文,根据短文中字母a,b出现的机会完成后面提出的问题:
Two Trips
Jack brought a small plane and began to fly it. He soon became excited and made his plane all kinds of tricks.
Jack had a friend,named Tom. One day Jack said to him,“I will pick you up in my plane.““I will be glad to.'answered Tom. They went up,and Jack flew around for half an hour and did all kinds of tricks in the air. Then they came down. Tom was to be back safely,and said to Jack,“Well,Jack,thank you very much for those two trips in your plane.“Jack was very surprised and asked,“Two trips?““Yes,my first and my last.'an﹣swered Tom.
根据上文填表
出现字母的个数
100
150
200
250
300
350
400
出现字母a的频数
出现字母a的频率
出现字母b的频数
出现字母b的频率
下列最容易腐败变质的食物是( )
“乌木”是( )