The letter is sent to you by airmail to Moscow every summer.
Каждое лето письмо отсылается тебе в Москву авиапочтой.
Is the letter sent to you by airmail to Moscow every summer? (общий вопрос)
What is sent to you by airmail to Moscow every summer? (вопрос с вопросительным словом what)
When is the letter sent to you by airmail to Moscow? (специальный вопрос)
The letter is sent to you by airmail to Moscow or to St Petersburg every summer? (альтернативный вопрос)
The letter is sent to you by airmail to Moscow every summer, isn`t it? (разделительный вопрос)