ANS:D - Assembler

Here variable, memory address, Register are operands used in assembly language.

Eg from the instruction set of microprocessor 8085.

MOV A , B : here a and b are registered.
ADD 2047H , D: here 2047 is a memory address.
MVI b, 02 : here b is registered and 02 is data.

Assembler is a different thing.