Which celis of the ovary are involved in the synthesis of estrogen?
I. Theca interna cells.
II. Granulosa cells.
III. Interstitial cells.
IV. Theca externa cells.

Options

A. All are correct
B. All are incorrect
C. I and II are correct
D. III and IV are correct

Answer

To answer the question about which cells of the ovary are involved in the synthesis of estrogen, we can analyze the options provided:

1. **Theca interna cells**: These cells are located in the ovarian follicles and are known to synthesize estrogen. They play a crucial role in the production of androgens, which are then converted into estrogens by granulosa cells.

2. **Granulosa cells**: These cells also play a significant role in the synthesis of estrogen. They convert androgens produced by the theca interna cells into estrogens, particularly estradiol.

3. **Interstitial cells**: These cells are primarily found in the testes in males and are responsible for producing testosterone. They are not involved in estrogen synthesis in the ovaries.

4. **Theca externa cells**: These cells form the outer layer of the follicle and do not have a direct role in the synthesis of estrogen.

Based on this analysis, the correct answer to the question is that the cells involved in the synthesis of estrogen are:

- **I. Theca interna cells**
- **II. Granulosa cells**

Thus, the correct options are I and II.

### Final Answer:
The cells of the ovary involved in the synthesis of estrogen are:
- I. Theca interna cells
- II. Granulosa cells