Why was the silk road closed during the tang and song dynasty?

Two types of survey questions are open questions and closed questions. an open question allows for any kind of response; a closed question allows for only a fixed response. an open question and a closed question with its possible choices are given below. list the advantages and disadvantages of each question. open question: what can be done to get students to eat healthier foods? closed question: how would you get students to eat healthier foods? 1. mandatory nutrition course 2. offer only healthy foods in the cafeteria and remove unhealthy foods 3. offer more healthy foods in the cafeteria and raise the prices on unhealthy foods what are the advantages of an open question?