Общий: Did Kate forget to send the letter yesterday?
Спец: When did Kate forget to send the letter?
What did Kate forget to do yesterday?
Альтерн: Did Kate forget or remeber to send the letter yesterday?
Did Kate forget to send the letter yesterday or the day before yesterday?
Разд: Kate forgot to send the letter yesterday, didn`t she?
Kate didn`t forget to send the letter yesterday, did she?
(К подлежащему: Who forgot to send thу letter yesterday?-She did.