Report-card comments that are specific and kind

Your notes: reading has improved a lot this term, rushes maths and makes careless slips. Which comment is best?

• A“A good student. Keep it up.”
• B“Needs to stop being careless in maths.”
• C“Mai's reading has grown a lot this term, and she now reads longer books on her own. In maths, slowing down to check each step will help her avoid small slips.”