I guess that it really depend on the schools. I hear that the recommendation letter shoud be no less than 1 page and each is focused one of your key advantages. Just for your reference. Why not ask the admission office for their advice?
Answering the questions is the best one but most schools understand how busy your recommender is so a letter is quite acceptable. I summarized the common questions from various schools and ask recommender to write only one letter when I applied. | 
