The answers are:
A. DNA replication in the nucleus of a cell
B. From one helix of DNA in a replication process, we get two: The DNA is a double helix and it consists of two strands of specifically connected amino-acids. When the time for replication comes, a set of enzymes unwind the two strands and leave them as a base for additional two strands attaching to them - the green line is an example of that. The free nucleotides - adenine, guanine, thymine and cytosine are left open and the enzyme called DNA-polymerase helps to produce a new strand on the template of the old parental one (one of the blue ones in the picture)
C. By the location on the smaller picture - replication takes place in the nucleus. And the most important hint are the letters A - adenine, G - guanine, T- thymine, and C-cytosine. A connects with T, and G connects with C.