DNA is composed of two complementary strands this is reflected in the fact of that

The number of adenines in one strand is equal to the number of thymines in the complemetary strand.

Explanation:

Deoxyribonucleic acid or DNA is a molecule that contains the genetic information in all living organisms. So it contains all the hereditary genetic information that has the instructions to development.  This DNA molecule consists of two strands that bond together to form a double helix structure. Each strand of DNA is made up of nucleotides which are basic chemical components made of a phosphate group, a sugar group and one of four types of alternative nitrogenous bases. The four types of nitrogenous bases found in the nucleotides are:

The sequence of these bases determines how genes are made, and each gene has different biological instructions to create proteins (that will have different functions in the organism). To form a DNA strand, the nucleotides are linked together in chains, alternating with the phosphate and sugar groups.

The nitrogenous bases are complementary between them. Adenine and thymine are complementary, as are guanine and cytosine. So since adenine is complementary to thymines, and cytosine is complementary to guanine, the number of adenines in one strand is equal to the number of thymines in the complemetary strand. And the number of cytosine is equal to the number of guanine.

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.