Justify the following statements and identify the correct combination of statements with respect to accounts in estimation and costing:

P: They are five classes of stores that can be defined in three categories.

Q: All materials recieved are examined, counted, or weighed and entered in Measurement Book as well as in the Goods Received Sheet (Form 10-B).

R: Issue of materials from stock should be made only on receipt of an Indent (Form-7).