Which of the following best describes the structural relationship between genes, chromosomes and DNA? A. Genes consists of two long strands of chromosomes, and each of these two strands consists of molecules called DNA.
B. Each DNA molecule consists of a number of pairs of genes, and each pair of genes on the DNA molecule is made up of chromosomes.
C. Each chromosome consists of number of DNA molecules, and each DNA molecule is made up of one to four different genes.
D. Each chromosome consists of a single long DNA molecule, and each gene on the chromosome is a particular segment of that DNA.

D.Each chromosome consists of a single long DNA molecule, and each gene on the chromosome is a particular segment of that DNA.

Explanation:  

A closed DNA molecule contains two strands of linear nucleotide sequences, and both DNA strands contain genes. These genes are DNA sequences that may be transcribed in messenger RNAs (mRNAs).

The cell nucleus contains chromosomes in which the double-stranded DNA molecules are packaged by specialized proteins (histones).  Moreover, there are organelles (mitochondria and chloroplast) that also contain genes which are transcribed in an analog mode to genes contained in the nuclear chromosomes.

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.