It is house built in 1935. I am planning to replace the ground floor living room carpet with laminate. After removing the carpet and underlayment, I didn't see the sub-floor but only a thin layer of plastics boards. I lift up some the plastic boards along the wall and found bricks only. I did not lift up other plastic board in the room but it felt same when step on them. The hall and dinning room connected to the living room use laminate now and the floors were on the same level, so I guess the structure is same. Does it mean the house does not have sub-floor on the ground floor? What are the bricks, basement or foundation?

The easiest way to find out is to lift up one of the bricks to see what's underneath.  Am I right in assuming that there is no mortar between the bricks? I suspect that the bricks might just be sitting on earth and that your plastic sheets are a form of damp-proof course.

Question is ...if so, is it working ?  Easiest ay to find out is to get a small sheet of polythene and lay it on top of the existing plastic sheets overnight.  If in the morning there is condensation underneath the polythene then the answer is No.