Body growth in adult Ascaris occurs due to cell enlargement and free nuclear division.

Explanation:
1. Cell Enlargement:
- In adult Ascaris, cell growth primarily occurs through cell enlargement.
- This means that the cells increase in size, leading to overall growth and development of the organism.
- Cell enlargement is a process where the cells increase in size due to the accumulation of cytoplasmic materials and organelles.
- This allows the cells to accommodate more cellular components and support the growth of the organism.

2. Free Nuclear Division:
- Along with cell enlargement, adult Ascaris also undergoes free nuclear division.
- Free nuclear division is a process where the nucleus divides without cytokinesis, resulting in the formation of multinucleated cells or syncytia.
- This process allows for the rapid increase in the number of nuclei within a cell without the formation of new cells.
- The multinucleated cells contribute to the overall growth and development of the organism.

3. Mitosis and Amitosis:
- The options a) Mitosis and b) Free nuclear divisions are incorrect.
- Mitosis is a type of cell division that occurs in somatic cells and is responsible for the growth and repair of tissues. However, it does not play a significant role in the body growth of adult Ascaris.
- Amitosis is a process of direct cell division without the involvement of spindle fibers or the formation of a mitotic apparatus. It is not involved in the body growth of adult Ascaris.

In conclusion, the body growth in adult Ascaris occurs primarily through cell enlargement and free nuclear division. These processes allow for an increase in cell size and the number of nuclei within a cell, contributing to the overall growth and development of the organism.