In the early 1960s a number of investigators conducted a series of elegant experiments that helped to decipher the genetic code. Which of the following describes a bona fide property of the genetic code?

a. The genetic code consists of overlapping codons.
b. The genetic code is a doublet code composed of two nucleotides per codon.
c. Spacers or markers separate codons from one another.
d. The genetic code consists of nonoverlapping codons.