Please help me check the two sentences. Which one is correct in grammar. " But lately I've started keeping a small study diary. I write down all I need to do and when it needs to be done by. " Is the sentence above correct in grammar? Should I change it into : " But lately I've started keeping a small study diary. I write down all I need to do and when they need to be done by. " ? Thank you , I am looking forward to seeing an answer! Haha😄😄😄