The works from the romantic period, the victorian era, and the modern era: describe the common themes from each era. then explain the main elements of the historical context that contributed to the themes in each era.

List the books/plays/poems you studied in your course. 

Then think about what 'themes' these literary works had in common -- whether it was poverty, or romantic love, or family ties, or injustice, or whatever. Then try to put the themes in the historical context for each of the time periods. 

The question can also be read as: which themes are common *within* each period. For example if all the Romantic works dealt with the supernatural, all the Victorian works dealt with social injustice, and all the Modern works dealt with multiculturalism. I doubt this was the case, but I don't know what books you studied in your class.

I hope my answer has come to your help. God bless and have a nice day ahead!