Select all that apply:
some rules to remember when reading topographic maps are
the elevations of contour lines must always be whole number multiples of the contour interval
the thin line separating two different rock units is a contact line
points inside a contour line are a higher elevation than the contour line
strike-and-dip symbols indicate the degrees of tilt of rock strata

The correct answers are:

- the elevations of contour lines must always be whole number;

- points inside a contour line are a higher elevation than the contour line;

The contour lines represent closed circular lines that are connecting dots with the same elevation. To be easier for the observer, as well as for calculation, the contour lines are always marked with whole numbers.

The points inside a contour line are a special sign that is used inside of the top contour line of a certain land feature. These dots have elevation that is not sufficient that another contour line can be put, but are higher than the contour line that is last in order, so they are marked with the exact number of their elevation which is most commonly not a whole number. They usually represent a peak.