Transitive verbs and direct object

A transitive verb is one that requires a direct object to complement it. If the main verb requires a direct object to complete the sentence then we are talking about a transitive verb.
Look at the following example:

NP = An 11-year-old Canadian Boy     (Subject) 

V (trans) = saved  (Verb) 

NP = his whole family (Direct Object)  

The direct object is something or someone who receives the action or was affected by the action.

“One way of identifying the direct object in a declarative sentence is by asking a question introduced by who or what followed by the operator and the subject. The object is the constituent that who or what questions:” (Greenbaum and Nelson 15). 

What (dO) did (Op) an 11-year-old Canadian boy (Subject) save?
His whole family (dO)

Note: Remember that a transitive verb must have a direct object.