Краткое пояснение: Необходимо раскрыть скобки, используя Present Perfect.
Разбираемся:
- A: I have just received (just/receive) a postcard from Mary. She's in Hawaii.
- B: Really? How long has she been (she/be) there?
- A: Have James and Lilly arrived (Lilly/arrive) in London yet?
Ответ: have just received; has she been; Have James and Lilly arrived