Select the true statement. a) rna is mostly single-stranded; dna is always double-stranded. b) rna and dna usually have identical nitrogenous bases. c) several types of dna regulate protein synthesis.

The correct answer is -

A) RNA is mostly single-stranded; DNA is always double-stranded.

Explanation:

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the two different forms of nucleic acid that carry the genetic information in the form of nucleotide sequences.

RNA is generally single stranded that is it has a single strand of nucleotide sequences (for example, genome of human immuno deficiency virus is single stranded RNA).

On the contrary, DNA always occurs in double stranded form (such as genetic material of human beings) that is it has two strands of nucleotide sequences, which are antiparallel or complementary to each other.

Thus, A) option is the right answer.