Please explain in detail why you chose each answer:

No written work.

19. Which of the following prevent duplicates of records? a. Unique Index b. Not Null c. Unique Data Type d. Binary Column 20. What is Float number? a. It includes a whole and decimal numbers (with 4 digits after the decimal point) b. It includes only decimal numbers (with 4 digits after the decimal point) c. It includes only a whole d. It includes all kinds of numbers and characters 21. Which data type should have a field "Course Number" in courses table? a. INT b. VARCHAR c. FLOAT d. DECIMAL The following information is for the next 3 questions. You were asked to build a database of an academic institution. You need to have several tables including one for Students, Courses, and Lecturers. 24. Which type of link you should establish between the courses table and the students table? a. Many-to-Many b. One to many (one from courses table to many in the students table) c. Many to one (from the courses table) to one (to the Students) d. There is no link between the courses table to the Students table 25. Which type of link you should establish between the students table and the lecturers table? a. There is no direct link between these two tables b. One to many (one from students table to many in the lecturers table) C. Many to one (many from the lecturers table) to one (to the Students table) d. Many to many 26. The students' table will includes information about the students. Which additional fields it should include? a. A link to a bridge table b. A foreign key to the courses table c. Primary key of the courses table d. No additional field is required