Throwing Exceptions in Apex:
throw new ExceptionType();creates a new instance and throws it.
A: No argument constructor.
B: Constructor with a custom error message.
Why Not Other Options?
C and D: These create exception instances but do not throw them, which is not valid syntax for firing an exception.
References:Apex Exception Handling:https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta
/apexcode/apex_classes_exception_methods.htm