The investigations conducted by Edwin Chargaff support the idea that DNA is the source of heritable information, and they also show a relationship between the ratios of the different nitrogenous bases in DNA. Based on the results of Chargaff's research, which is the best estimate of an organism's DNA base composition that contains 28.0% thymine

all the thymine pairs with adenine, therefore there is the same number of adenine and thymine bases and the same percentage

so we have 28%thymine and 28% adenine

100-28-28=44% left

this 44% is guanine and cytosine. All of the guanine pairs with cytosine and all of the cytosine pairs with guanine so we have 44/2=22% cytosine and guanine

composition:

28%adenine

28%thymine

22%guanine

22%cytosine

i believe the answer would be b. hope it : )