(More aggregation with grouping) Based on the conference database on the website, and using WHERE to express joins between tables, write SQL queries for the following tasks: A For each room in which any session is being held, show the room ID and the number of sessions being held there (with the column heading NumSessions). B Show the same information as part (a), but also show the capacity of each room. C For each room, show its ID, capacity, and the number of presentations being given there (the heading for this column should be NumPresentations). D For each speaker, show their first name, last name, the number of  presentations they are giving (with the column heading NumPresentations). Make sure that if the conference were large enough to have two speakers with the same name, each would appear on a different line of the output.