Step 1: Understanding the Question.
We are given one sentence and must decide which statement is definitely true, based only on the wording of that sentence, not on any outside assumption.
Step 2: Key Approach.
The sentence follows the pattern "If + past perfect, would have + past participle", called the third conditional. This grammar pattern is used only to talk about an imagined, different past, one that did not actually happen. When we say "if X had been true, Y would have happened", we are stating that, in reality, X was NOT true, and so Y did not happen either.
Step 3: Detailed Explanation.
Here the "if" part is "his latest movie had been a commercial success". Because the third conditional describes an imagined alternative to what really happened, this tells us that, in reality, his latest movie was NOT a commercial success.
Now check each option:
(A) says the actor "will certainly sponsor" his next movie. This talks about the future with certainty, but the sentence only describes an imagined past scenario; it makes no promise about what will actually happen next, so this cannot be concluded.
(B) says the movie "was a commercial success". This is the exact opposite of what the third conditional tells us, since the "if" clause describes something that did not really happen.
(C) says the actor "made enough money". Since the movie was not a commercial success, he did not make that money, so this is false.
(D) says the movie "was not commercially successful". This matches directly what the third conditional implies about the real past, so this is the statement we can be sure is true.
Step 4: Final Answer.
Since the sentence uses a third conditional (an unreal past), the real situation is the opposite of the "if" clause. His latest movie was not commercially successful.
\[ \boxed{\text{His latest movie was not commercially successful.}} \]