The true statement about chromosomes is: Chromosomes contain DNA.
The other statements are incorrect. Chromosomes are not found in sets of three; they come in pairs in diploid organisms (such as humans, who have 46 chromosomes organized into 23 pairs), and the number of chromosomes in haploid cells (like sperm and egg cells) is half that of body (diploid) cells. Additionally, DNA does not contain chromosomes; rather, chromosomes are structures made up of DNA and proteins.