4. Susan .......... (do) her homework before 10 o'clock but Jane .......... (not / write) a word until now.

Решение:

1. had done — Past Perfect, так как действие ('сделала домашнее задание') произошло до другого действия в прошлом ('до 10 часов').
2. has not written — Present Perfect, так как действие ('не написала') продолжается до настоящего момента ('until now').

Ответ: Susan had done her homework before 10 o'clock but Jane has not written a word until now.