Explanation:

- Allen: Allen is known for his contributions to legal theory and philosophy, but he's not the key figure related to the sociology of law in this context.

- Friedmann: A prominent legal scholar who wrote extensively on the sociology of law, including critiques and development of legal theories with respect to societal contexts.

- Paton: He focused on jurisprudence and the philosophy of law, as seen in his work "A Textbook of Jurisprudence".

- Salmond: Known for Salmond on Jurisprudence, contributed significantly to the legal theory and legal research methodology.

- Correct Answer: Friedmann is the one who expressed the idea that Enrilch's sociology of law could turn into a broad sociology.