Consider the following statements:
P. Walls of one brick thick are measured in square meters.
Q. Walls of one brick thick are measured in cubic meters.
R. No deduction in the brickwork quantity is made for openings in walls up to 0.1 $$m^2$$ area.
S. For the measurement of excavation from the borrow pit in a fairly uniform ground, dead men are left at suitable intervals.
For the above statements, the correct option is