You must find the number of employees whose salary is lower than employee 110.

In this context, the correct answers will provide a count of employees with a salary less than that of employee with ID 110. Let's evaluate the provided statements:

A: This statement is incorrect due to a syntax error; it uses alias 'e' without defining it, and 'a' is also used incorrectly in the JOIN clause. It should have been written with proper aliases.

B: This statement is correct as it uses a subquery to find the salary of employee ID 110 and compares it to the salaries of all employees to get the count.

C: This statement is also correct as it creates a derived table with the salary of employee ID 110 and compares it with the salaries of the 'employees' table using a JOIN.

D: This is the statement that fails. It is incorrect because the subquery references 'e.employee_id = 110', which will compare the salary of each employee to themselves if their ID is 110, not to the salary of employee 110 for all employees.