Many Images of the Chromosphere Are Taken Through a Filter

Many images of the chromosphere are taken through a filter that allows only specific wavelengths to pass. One reason for this is

A) to block out all other wavelengths of light and allow through the prominent light of these wavelengths produced in the chromosphere.
B) to allow through the filter the background light at these specific wavelengths produced by the photosphere and thus show an effective contrast with the chromosphere.
C) to ensure that Earth's atmosphere does not interfere with the image.
D) to block out light from the corona.