I am new to this site, so bear with me. I believe it would be more appropriate to word those Sentences as follows: Nowadays our flourishing civilization has a lot of problems. We must realize that our terrible actions against Earth are not justifiable. I don't think you need to say "After all", as you are not trying to state that something exists in a certain condition. For more on the use of the 'Idiom' "After all" read the explanation found here: http://answers.yahoo.com/question/index?qid=20071031090409AAsScDt Instead of using "the Earth" just use "Earth", because "The" is not used with non-countable nouns when you are talking about and referring to something in a general way. For more information explaining how this works check out this page: http://www.english-test.net/forum/ftopic7920.html Also if you are writing to make a point, and you want it to have a mildly greater impact on the reader then try wording the second sentence as follows: We must realize that our terrible actions against Earth are in no way justifiable.