Choose the correct passive voice: He published his second book on gender inequality.

His second book has been published by him on gender inequality.

His second book is published by him on gender inequality.

His second book was published by him on gender inequality.

None of these

The original sentence is in simple past tense: "He published..."

The passive voice of a simple past sentence follows the structure: Object + was/were + past participle + by + subject

Therefore, "His second book was published by him..." is correct.