1) Why
Ответ: Because they have to go to work.
2) What
Ответ: He bought some sweets.
3) When
Ответ: She made a cake two hours ago.
4) Who
Ответ: My brother was six year old.
5) How many
Ответ: Six people came to see the grandma and the grandpa?
Насчёт последнего не особо уверена.