Which enzyme is responsible for linking the fragments of $DNA$?

Identify parts $A, B, C, D$ in the figure given below:

Which organism was used as experimental material to study $DNA$ replication?

Experiments involving the use of radioactive thymidine to detect the distribution of newly synthesized $DNA$ in the chromosome were performed on which plant?

$DNA$-dependent $DNA$ polymerase catalyzes polymerization in which direction?

Okazaki fragments are observed in which of the following processes?