The grammar of English English textbooks say that the grammar of the following two sentences are right; 1, There is a sleeping boy. 2, There is a boy sleeping in the bed. They also say that the following two are wrong; 3, There is a boy sleeping. 4, There is a sleeping boy in the bed. I couldn't tell a difference between them. The latter two sentences sound strange? or don't make sense? ...or no problem?

Does this sentence sound strange? Hello, I'm Japanese student and learning English. In a class, I was assigned to translate a sentence in a paper into English. I gave it a try, but I couldn't confirm whether it is right or not. Would somebody judge following sentence please? ************** The cause of the observed low strength is attributable to sulfur contained in the alloy at 0.001%. ************** In this sentence, I want to express these points. 1. Sulfur is 0.001% of the alloy. 2. Sulfur caused the alloy to decrease its strength. I hope to get your corrections or better expressions(of course, for the whole sentence too if possible). Thank you so much for your read.