I have got C grade in three subjects and D grade (in last attempt) in remaining subject. Even then I am not declared pass. Why?

For  PASS, you must get B grade in at least one subject (Section A, Diploma Stream) to make total GPA equal to 6 or more.

Examples:

(1) C, C, C, D (D in last attempt). You have to reappear in subject with D grade

(2) C, C, B, D (D in last attempt). PASS

(3) C, C, C, C. PASS

To know GPA calculation method, click here

To convert GPA to percentage, click here