Mr Khanna had a pond in his garden, filled with all kinds of aquatic plants. He wanted to prevent mosquitoes from breeding in the pond without harming the plants in any way. He could _______.
(i) Add salt into the water
(ii) Add some goldfish into the pond
(iii) Spray a film of oil on the surface of the pond

Options

A. (i) only
B. (ii) only
C. (iii) only
D. (i), (ii) and (iii)

Explanation

To solve the problem of preventing mosquitoes from breeding in Mr. Khanna's pond without harming the aquatic plants, we need to evaluate the three options provided:

1. **Add salt into the water**:
- Adding salt to the pond water would likely harm the aquatic plants. Most freshwater plants are not adapted to high salinity levels, and introducing salt could lead to their death or stress. Therefore, this option is not suitable.

2. **Add some goldfish into the pond**:
- Goldfish are known to eat mosquito larvae. By introducing goldfish into the pond, they will consume the larvae, effectively reducing the mosquito population without harming the plants. This option is beneficial and aligns with Mr. Khanna's goal.

3. **Spray a film of oil on the surface of the pond**:
- While spraying oil can create a barrier that prevents mosquito larvae from breathing, it can also harm aquatic plants by blocking sunlight and oxygen exchange. This option could negatively affect the health of the plants in the pond.

Based on the evaluation of the three options, the best choice for Mr. Khanna to prevent mosquitoes from breeding in his pond without harming the plants is to **add some goldfish into the pond**.

### Final Answer:
Mr. Khanna could **add some goldfish into the pond**.