Answer:
They both are considered high holy days
Explanation:
Rosh Hashanah is basically the beginning of the new year according to Jewish meaning, and generally believed or considered to be one of the holiest days of the year in Judaism.
At the same time, Yum Kippur is also considered to be atonement day, to the Jewish people.
Hence, element that Rosh Hashanah and Yom Kippur shared is that : they both are considered high holy days
