Concept:
Wittgenstein emphasized language-games, forms of life and social practices.
For him, meaning and knowledge are not isolated private matters.
They are connected with public use and shared practices.
Step 1: Understand belief as knowledge claim.
A belief becomes a knowledge claim when it functions within a public language-game.
It must be capable of being expressed, understood and accepted within a shared form of life.
Step 2: Reject purely subjective acquisition.
If something is only privately or subjectively acquired, it does not automatically become a knowledge claim.
Knowledge requires public criteria.
Step 3: Understand social acceptance.
According to Wittgenstein, our claims of knowledge are grounded in socially accepted practices and forms of life.
So, social acceptance plays an important role.
Step 4: Final conclusion.
Therefore, a belief becomes a knowledge claim when:
\[
\boxed{\text{It is accepted socially}}
\]
Hence:
\[
\boxed{\text{(D)}}
\]