Read this: Roman calendars show roughly forty annual religious festivals. Some lasted several days, others a single day or less: sacred days (dies fasti) outnumbered "non-sacred" days (dies nefasti). A comparison of surviving Roman religious calendars suggests that official festivals were organized according to broad seasonal groups that allowed for different local traditions. Some of the most ancient and popular festivals incorporated ludi ("games," such as chariot races and theatrical performances), with examples including those held at Palestrina in honour of Fortuna Primigenia during Compitalia, and the Ludi Romani in honour of Liber. Other festivals may have required only the presence and rites of their priests and acolytes, or particular groups, such as women at the Bona Dea rites.

Instead of the public, what did some religious rites only require?
What is the answer? (If it cannot be answered, return "unanswerable")
particular groups