Explanation:

- The maximum period of detention in civil prison when the decree is for more than Rs.5,000 is governed by Order 21 Rule 40 of the Code of Civil Procedure (CPC), 1908.

- Let's look at the options:

- Option 1: Six weeks – Detention up to six weeks is allowed if the decree amount does not exceed Rs.2,000.

- Option 2: Two months – This period is not generally prescribed under CPC for decree over Rs.5,000.

- Option 3: Three months – Also not the correct maximum detention period for decrees over Rs.5,000.

- Option 4: Six months – This is the correct maximum period allowed for detention if the decree amount is more than Rs.5,000.

- The law provides a maximum of six months of civil detention in such cases.