Modify Sick Sentence: The classroom erupted in applause after Mr. Wang finished his story.

This sentence, taken as a whole, shouldn't be considered a sick sentence, just lacking in embellishment. But look at it separately and you can pick out the problem. In the first clause, "teacher, tell, story" is the subject of the predicate-object; in the second clause, "loud, applause" is the predicate-object, the subject? No. "In the classroom" is actually a prepositional phrase, omitting "in". If the teacher insisted that you change it, you would change it to: "After Mr. Wang finished the story, the students in the classroom applauded loudly."