The correct answer is $\boxed{\text{C}}$, 60°.
A circumpolar star is a star that never sets or rises for an observer at a particular latitude. This is because the star’s declination is greater than the observer’s latitude. The declination of a star is its angular distance north or south of the celestial equator.
The altitude of a star is its angular distance above the horizon. The altitude of a circumpolar star at culmination is the maximum altitude that the star reaches in the sky.
The latitude of a place is the angle between the Earth’s equatorial plane and the vertical at that place.
The altitude of a circumpolar star at culmination is equal to the observer’s latitude plus the star’s declination.
In this case, the altitudes of the circumpolar star at culmination are 70° and 10°. This means that the star’s declination is 70° – 10° = 60°.
Therefore, the latitude of the place is 60°.