Final answer:
d) Heat or NaOH can be used to separate the DNA double helix into single strands.
Step-by-step explanation:
The DNA double helix can be separated into single strands using heat or NaOH. Exposing the DNA strands to high temperatures can break the hydrogen bonds between the complementary bases, separating the strands into single strands of DNA. Similarly, treating the DNA with a strong alkaline solution, such as NaOH, can also denature the DNA by disrupting the hydrogen bonds. Both heat and NaOH can be used to denature DNA and study its structure and function in the laboratory.