For a computer based on 3-address instruction formats, each address field is used to specify which of the following
S1: A memory operand
S2: A processor register
S3: An immediate constant data
Which of the following statements are correct?
a) Either S1 or S2
b) Either S2 or S3
c) Only S2 or S3
d) All of S1, S2 and S3