Here are the answers for each part of your questions:
**Part : In a DNA double helix, an adenine of one strand always pairs with a(n) **thymine** of the complementary strand, and a guanine of one strand always pairs with a(n) **cytosine** of the complementary strand.
**Part B**: After DNA replication is completed, **each new DNA double helix consists of one old DNA strand and one new DNA strand**.
**Part C**: The first step in the replication of DNA is catalyzed by **helicase**.
**Part D**: The action of helicase creates **replication forks and replication bubbles**.
**Part E**: The new DNA strand complementary to the 3' to 5' strand is assembled in short segments because **DNA polymerase can assemble DNA only in the 5' to 3' direction**.
**Part F**: The synthesis of a new strand begins with the synthesis of a(n) **RNA primer complementary to a preexisting DNA strand**.
**Part G**: An old DNA strand is used as a **template** for the assembly of a new DNA strand.