Answer:
C.
Explanation:
I usually get told this is incorrect from the point of view of someone else who has been corrected multiple times in the past. Understandably, if Tammy doesn't like you, you wouldn't tell her.
But, in a perfect world, this is [ideally and probably] the best way. Letting Tammy know "hey, this is how to improve" is better than humiliating her in front of her friends and the teacher and ultimately bringing down her confidence. Direct correction might work better because then she will see her mistakes and be told how to fix them for her future reference.
Remember: Writing is thinking. Writing is literally just translating the words you're thinking into words on a page/computer or other media.
If she [Tammy] is offended, talking to the teacher may be the best way so the teacher can handle it.
