The colums in any data table represent blank in a controlled experiment

hello which   of the following there is nothing!

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides

bradykinin is a physiologically and pharmacologically active peptide of the kinin group of proteins, consisting of nine amino acids.

the answer is 100% density i've answered this question before and done the quiz myself.