sentence: Imagine this picture : the first class of this semester , students are yawning and do not pay attention to the teacher , while the teacher asks for the answer , students can not answer because they totally can not remember what they studied last semester .
modified: Imagine this picture : the first class of this semester , students are yawning and do not pay attention on the teacher ; while the teacher ask for the answer , students can not answer because they totally can not remember what they have studied in last semester .
transformation: PREP, PUNCT, VERB:SVA, VERB:TENSE, PREP