After the bases of DNA were identified, Erwin Chargaff analyzed the percentages of adenine, thymine, guanine, and cytosine in the DNA of many different organisms. This table shows the percentages of A, T, G, and C for a human, a bacterium, and a fish. Chargaff observed an approximate rule about these percentages in all of his samples: What is the rule?

A.
A + T = G + C

B.
A = G; T = C

C.
A = C; T = G

D.
A = T; G = C

D) A = T; G = C

Explanation:

Chargaff's rules state that "DNA from any cell of any organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine".

This pattern is noticed in the DNA strands.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".