Study the following and pick up the correct combinations:

Thus, the correct answer is Option (D).
| List - I | List - II |
|---|---|
| A. Progesterone | IV. Corpus luteum |
| B. Relaxin | II. Ovary |
| C. Melanocyte stimulating hormone | III. Adrenal Medulla |
| D. Catecholamines | I. Pars intermedia |
Two concentric thin circular rings of radii 50 cm and 40 cm each, carry a current of 3.5 A in opposite directions. If the two rings are coplanar, the net magnetic field due to the two rings at their centre is: