Select the number from among the given options that can

Which database model represents data in a tree-like structure, where each child record has only one parent?

Which of the following is a common technique for concurrency control in databases?

Which interrupt is generated by software?

Which isolation level allows dirty reads?

Consider the following Java code snippet 

public class Car {

    private String model;

    private int year;

Which SQL isolation level allows phantom reads but prevents dirty reads and non-repeatable reads?

Query optimization heuristic that “pushes selections down” improves:

Which SQL command is used to retrieve data from a database?

In the context of database transactions, which isolation level allows "non-repeatable reads" but prevents "dirty reads"?

Which SQL clause is used to group rows based on one or more columns?