Explanation:

- Option 1: Domes – Domes are a distinctive and integral element of Indo-Islamic architecture. They can be seen in many structures like mosques, tombs, and forts.

- Option 2: Shutter windows – These are not a signature feature of Indo-Islamic architecture. They are more common in colonial or later architectural styles.

- Option 3: Tall and steep slopes – Such slopes are not characteristic of the Indo-Islamic form, which preferred balconies, arches, and domes.

- Option 4: Square roofs – Indo-Islamic architecture is famous for its arches and domes rather than flat or square roofs.