1.Describe the four levels of isolation in SQL. 2. Define the violations caused by each of the following: dirty read, nonrepeatable read, and phantoms. 3.. Add the operation commit at the end of each of the transactions T[ and Tz from Figure 17.2; then list all possible schedules for the modified transactions. Determine which of the schedules are recoverable, which are cascadeless, and which are strict. 4 .List all possible schedules for transactions T[ and Tz from Figure 17.2, and determine which are conflict serializable (correct) and which are not.