This is a very wide topic, and I don't have an answer for these questions.
这是一个很广泛的课题，而且对于这些问题我一直找不到答案。
This is a fills up the topic, I think of that thing has the answer, so not hesitate to fill in the environmental protection.
这是一道填空题，我一想起那件事便有了答案，于是毫不犹豫的填上了环保两个字。 。
I googled a long time on the Internet in order to answer his question. Then I discovered a U. S. professor who lectures on this subject. She has even written a book on this topic.
为了回答这个问题我在网上找了好久，最后发现一个美国教授就这个问题专门开了一门课，还写了专著。
应用推荐