Question

is shaped like a double - helix, where two chains of nucleotides form a spiral.
a trna
b rna
c mrna
d dna

Explanation:

• tRNA (Transfer RNA): It has a clover - leaf - like structure, not a double - helix. It is involved in transferring amino acids during protein synthesis.
• RNA (Ribonucleic Acid): In general, RNA is usually single - stranded (although some regions can have secondary structures like hairpins). For example, mRNA (messenger RNA) is mostly single - stranded.
• mRNA (Messenger RNA): It is a single - stranded molecule that carries genetic information from DNA to the ribosome for protein synthesis.
• DNA (Deoxyribonucleic Acid): According to the Watson - Crick model, DNA is composed of two chains of nucleotides. These two chains are anti - parallel and form a double - helix structure through hydrogen bonding between complementary base pairs (adenine - thymine and cytosine - guanine).

Answer:

d. DNA