Final answer:
The correct answer is (A) Portions between centromeres and telomeres, as euchromatin is found in these less condensed regions and contains actively transcribed genes, whereas centromeres and telomeres are composed of more tightly packed heterochromatin.
Step-by-step explanation:
The following is composed of euchromatin is (A) Portions between centromeres and telomeres. Euchromatin is the less dense region of the chromosome, where DNA is packaged around nucleosomes but not further compacted, usually containing genes that are actively transcribed.
In contrast, heterochromatin is more tightly packaged and is typically found in the regions of the centromere and telomeres, containing genes that are usually not expressed. Interphase chromosomes display these two distinct regions, with euchromatin being the areas where transcription is active, allowing the necessary space and accessibility for the transcription machinery to do its job.