**Core Concept**
Hybridoma technique is a method used in molecular biology to produce large quantities of specific antibodies. It involves the fusion of B cells, which produce antibodies, with myeloma cells, which are capable of immortal growth, to create hybrid cells that can produce antibodies indefinitely.

**Why the Correct Answer is Right**
The hybridoma technique is used to obtain monoclonal antibodies, which are antibodies produced by a single clone of B cells. This results in a homogeneous population of antibodies with the same antigenic specificity. The myeloma cells provide the necessary genetic material to support the growth of the hybrid cells, while the B cells provide the ability to produce antibodies. The resulting hybrid cells can be cultured in vitro and produce large quantities of the desired antibody.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the hybridoma technique is not used to obtain polyclonal antibodies, which are a mixture of antibodies produced by different B cells.

**Option B:** This option is incorrect because the hybridoma technique is not used to obtain activated T cells, which are a type of immune cell that plays a key role in cell-mediated immunity.

**Option C:** This option is incorrect because the hybridoma technique is not used to obtain cytokines, which are proteins produced by immune cells that play a key role in immune responses.

**Clinical Pearl / High-Yield Fact**
The hybridoma technique has revolutionized the field of immunology by enabling the production of large quantities of specific antibodies, which have numerous applications in research, diagnosis, and treatment of diseases.

**Correct Answer: D. Monoclonal antibodies**