Решите пожалуйста с объяснением!

You needn't be afraid of exams. They are aimed at identifying your level of knowledge and skills (я хз, вообще в этом предложении должен быть should not)
We needn't to learn the whole rule, just parts a and b - не нуждаются в этом
Need I repeat my question, class? No, you doesn't need. Everything is clear. Нет нужды в этом
Need we stay here longer. Yes, you need. The exam isn't over yet. Есть нужда
Boys, I need your help. No problem. What do we need to do? 1 - Есть нужда, 2 - мальчики самыми вызвались
Must we do our homework for tomorrow Yes you must - обязанность
Do we need to do it at home? - нужда
She need not (must not, I suppose)to finish the test right now. If she needs to leave - нужда
Sarah need not to get up early, but she must to help her brother - обязанность
Do you go? Yes, I do - действие