Which of the following accurately describes the structure of dna?
a. dna is made up of nucleotides, containing a 3-carbon sugar, a phosphate group, and base.
b. a always pairs with c, and g always pairs with t.
c. dna consists of four bases: a, g, c, and u.
d. dna is in the form of antiparallel strands twisted as a double helix.

Cladistics is a way of classifying organisms by examining the characteristics of their ancestors and descendants and depicting the relationships in a cladogram. which of the following best describes a challenge in classifying organisms this way? a. there are millions of species on earth, and a cladogram is not a practical means for classifying all of them. b. it is impossible to tell which organisms are most closely related to each other using a cladogram. c. cladograms are detail-oriented and do not provide a useful understanding of evolutionary relationships. d. there is a limited number of ways to organize the information, so most cladograms end up looking very similar.