D- a bond in which electrons are transferred
The right option is a. contour interval
The difference in elevation between the highest and lowest contour lines on a topographical map is called contour interval.
A contour interval is the vertical distance between the two contour lines (highest and lowest) in a topographical map. The contour interval is usually stated explicitly on the right-hand lower part in every map. 20 feet for a 1:24,000 map scale is the frequently used contour interval and different contour intervals is available for different maps.
The right answer is Filtration.
A water filter is composed of a filtration system that aims to separate the water from the solid particles (residues) by passing it through a porous medium, which allows only the liquids and the finer solid particles to pass through. as the filter holes (porosity). The water that comes out of this filtration system is rid of solid particles larger than the pores of the filter.
Some water filters are designed to make drinking water (very fine filtration, less than the size of a microbe).