LW R1 , 20(R2)
options A,B are anyway out of the context.
first of all in such writings 2 symbols directly means indirect , 1) @ 2) ( );
2nd of all in base addressing or based indexed addressing we do not I REPEAT we do not use the base value like this.
i dont know if option C is correct or not..
but D can't be the answer...
in based indexed addressing we must use 2 registers... giving 20 directly is not fulfilling the rules.
(Effective address = contents of specified base register + contents of specified index register)
Based Indexed Addressing: The operand’s offset is sum of the content of a base register BX or BP and an index register SI or DI.
Example: ADD AX, [BX+SI]