He bought new shoes last month but they are already . . . . . . . . out.

The correct answer is D. worn.

The other options are incorrect because:

• A. given: The shoes are not given out. They are worn.
• B. gone: The shoes are not gone. They are worn.
• C. knocked: The shoes are not knocked. They are worn.

The sentence “He bought new shoes last month but they are already worn out” means that the shoes are no longer in good condition because they have been used a lot. The shoes are probably dirty, scuffed, and have holes in them.