Many Images of the Chromosphere Are Taken Through a Red

Many images of the chromosphere are taken through a red filter.One reason for this is to:

A) block out all red light and allow through the prominent light of other colors produced in the chromosphere.
B) allow through the filter the red light produced by the photosphere and thus show an effective contrast with the chromosphere.
C) ensure that the blue of Earth's atmosphere does not interfere with the image.
D) allow through the red light which is produced predominantly in the chromosphere and not in the photosphere.