The right answer is D.
In plants, we find three types of DNA: genomic, mitochondrial and chloroplast DNA. Only DNA possess thymine in its composition. So, the radiolabelled thymine indicates the presence of the DNA.
*The chloroplast is a plant organelle containing chlorophyll and DNA, the seat of photosynthesis.
*Mitochondria is a cellular cytoplasmic organelle that plays an essential role in respiratory and energetic phenomena, it contains enzymes as well as its DNA (mitochondrial).
*At the nucleus, we find genomic DNA.
