What started the feud between the Capulets and Montagues?

Romeo killed Tybalt.

Capulet challenged Montague to a duel and Montague never showed up.

Capulet was in love with Lady Montague before she married Montague.

The text does not say.

The text does not say that what was the reason that started the feud between the Capulets and Montagues. So, here the answer would be Option D.

Explanation:

Shakespeare's "Romeo and Juliet," is a narration of how two lovers are doomed due to the ongoing war struggle between the two families the Capulets and Montagues. The play starts with a feud between the noble families but the reason why they are enemies is not known. It is the dispute between them that is covered in all the major events of the play. This deep-rooted struggle between the families for generations is what leads to the tragic deaths of the lovers - Romeo and Juliet from the two respective Houses. It is after this that the families bury their enmity and mourn.