A is correct: DNA is indeed found in the nucleus of eukaryotes.
B is incorrect: Although there can be single strands of DNA (ssDNA), DNA is usually double-stranded which is how it forms its characteristic double-helix shape.
C is correct: Deoxyribose is indeed the sugar in DNA (Deoxyribonucleic Acid)
D is correct: The two single ringed nitrogenous bases in DNA are thymine and cytosine, while the other two (Adenine and Guanine are double ringed.
