众所周知孩子是妈妈的时尚单品

你好。答案是AS
== It is well known that the environment in China is badly in need of improvement.
== the environment in China is badly in need of improvement, which is well known.
== that the environment in China is badly in need of improvement is well known.
== what is well known is that the environment in China is badly in need of improvement.
== the environment in China being badly in need of improvement is well known.

翻译：众所周知，中国的环境质量急需改善/提高。

---

　　因为它冗余选择C
As is well-known, the environment in China is badly in need of improvement.
众所周知。
D要成立的话，需要改成What is well known is that the environment in China is badly in need of improvement.即使这样也不是一个好句子。

---

　　选择C
As is well-known, the environment in China is badly in need of improvement.
众所周知，中国的环境亟需改善。

这是As引导的非限制性定语从句，修饰后面的主句，放在主句前面用As，放在主句后面可以用which和as。
A,B选项要成立的话和后面句子缺少连词and。
D要成立的话，需要改成What is well known is that the environment in China is badly in need of improvement.即使这样也不是一个好句子，因为它冗余。

希望对你有所帮助。如满意请点击下面的“选为满意答案”按钮，谢谢您！

---

　　答案：C
翻译：As is well-known, the environmentin China is badly in need of improvement.
众所周知，中国环境急需改善。
分别用A和D选项改写句子（保持原意的前提下）如下：
A.It ——It is well-known that the environmentin China is badly in need of improvement.
D.What——What is well-known is that the environmentin China is badly in need of improvement.

仅供参考，O(∩_∩)O~

---

　　C
引导非限制性定语从句，用来指代整个句子(即先行句)，意思是“这一点”。这个分句可以位于句首、句中或句末。eg：
As is well known，oceans cover more than 70％ of the earth．我们知道，海洋占地球面积的百分之七十以上。
be in badly need of.....急需.......(可作为固定短语)
众所周知，中国的环境急需改善。

---

　　楼主好,

选C as

As is well-known, the environment in China is badly in need of improvement.
众所周知. 中国的环境质量是急需提高的.

希望对你有帮助^^