sign and Calculation Questions: 19. (30 pts) Suppose you are given the following requirements for a simple database for Twitter messages: there are many Twitter accounts and many messages each account has an account ID, name, location, account description, and many received messages each message has a message ID, creator account ID, creation time, textual message one message belongs to only one original creator account one message can be delivered to multiple accounts at different times one message can belong to multiple accounts(followers) Construct a clean a nd concise ER diagram for this database using the notation as in the lecture note. Explain your assumptions in your ER diagram. 0. (10 pts) Consider two hard disks, A and B. Both have 100,000 tracks per a surface but A has 2000 sectors of 4Kbytes per track while B has 1000 sectors of 16 Kbytes per track. Both disks rotate at 7,200 RPM. Assume the disk has a bandwidth of 100MB/sec