1.Ever since Dolly,the sheep ___in 1997,many scientists have been working on cloning a human being.A had cloned B has been cloned Cwould cloned D was cloned2.The theory ___ about in 1514,but the csirntist only published it just defore his death in 1543.Ahad put forward Bwas put forward3.In American English,the letter"u" in some words,such as colour,___Ais dropped Bare dropped正确答案是D B A 但理由是什么？

1、选D原因，自从多利绵羊在1997年被克隆以后，.......讲述的是过去的一件事情，因此用过去式was cloned。
2、同上。
3、“u”为元音字母，不是单词中的元音音标，只有元音音标后面用are。

1. D
2. A
3. B
不好意思, 中文不太好, 希望你能懂
第一句, A 跟B 都不行 因为后面用了have been, 就是说, 这还在进行中
一句话不能有2个进行中的过去式 如果有这个过去式在一句话里面, 发生第一的那句就用 had + 过去分词,然后第二样过去事情就用过去式. 例如:
The theory had put forward....... but the csintist only published it....
就像第一个问题一样
那我写几句简单例子:
i had thrown the ball into the trash can, but it disappeared in a hour
i had finished my homework, and i ated dinner with my family.
第一句, 仍球是第一件事情, 它消失是后来的
第二句, 做完作业后 我才吃饭
这让, 人家就明白你哪件事情发生第一
你的第3个问题就不用说了
in letter"u" in some words,
some words 是负数 看句子一定要找出它想说的意思
它不是要说the letter,它是说 some words带有u的, 那就多于一个,应为是words, 而不是word
那就用are
such as 就是举例
给你一个例句
i have some books, such as math, english, history, are still very new

1D ever since 后面的从句用一般过去时
2B but 连接的是两个并列的分句 ,所以but 前后连接的两个句子的时态应该一致,所以选B 用过去时的被动语态
3A 句子的主语应该是the letter"u" 所以谓语动词要用单数 选B

1.Ever since Dolly,the sheep _D__in 1997,many scientists have been working on cloning a human being.
A had cloned B has been cloned Cwould cloned D was cloned
2.The theory _B__ about in 1514,but the csirntist only published it just defore his death in 1543.
Ahad put forward Bwas put forward
3.In American English,the letter"u" in some words,such as colour,_A__
Ais dropped Bare dropped
希望能够帮到楼主