Step 1: Sources of authority.
The Dharmasutras and Dharmashastras are ancient Hindu legal and religious texts. They prescribed rules of conduct, duties, and social norms, including the institution of marriage.
Step 2: The eight forms of marriage.
The texts recognise eight types of marriage:
1. Brahma Vivaha
2. Daiva Vivaha
3. Arsha Vivaha
4. Prajapatya Vivaha
5. Gandharva Vivaha
6. Asura Vivaha
7. Rakshasa Vivaha
8. Paisacha Vivaha
Step 3: Conclusion.
Thus, according to Dharmasutras and Dharmashastras, there were eight forms of marriage.
\[
\boxed{\text{Correct Answer: Eight}}
\]