Evaluate this SQL statement: 
What is its output?（） 
（单选题）
Examine the data of the EMPLOYEES table. EMPLOYEES (EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID) 
Evaluate this SQL statement: 
What is its output?（）
A
B
C
D
E The SQL statement produces an error.
正确答案
答案解析
略
