Correct : b

Eliminating wrong options:
Option A - "People do not care about money" is incorrect. The passage says wallets with money are more likely to be returned, which means people do care about the owner's loss, not that they ignore money.
Option C - "Wallets used in experiments are more likely to be returned" is not mentioned anywhere in the passage. This is outside the scope.
Option D - "Money is always more important than keys" is incorrect. The passage actually shows the opposite — a key adds more reason to return the wallet.
Option B - The passage states the primary reason is compassion and empathy. A key suggests someone is locked out and suffering. People relate to that suffering and are therefore more likely to return it. This directly aligns with the passage's conclusion.
The correct logical inference is "Wallets with a key are more likely to be returned because people relate to suffering of others." (Option B)