Which of the following best reflects the addressing mode implemented by this instruction for the operand in memory?
"best reflects" doesn't imply that it must be exactly that implementation..
Keeping that in mind, and also that options A and B could not be the candidates,
Let's focus on $option \; C$ and $option \; D$
There is no literature that I found on the so called Indirect Scaled addressing..
There's nothing called Indirect Scaled Addressing, There is only scaled Base addressing where the scale is the number of bytes per offset..
But if we assume it exists and is similar to the Base Indexed addressing, then we have two valid interpretations, where both are consistent..
$R_1 \leftarrow (A+(R_0))$ or $R_1 \leftarrow (20+(R_2))$ Base Indexed addressing, where 20 is assumed to be the base address
$R_1 \leftarrow ((R_2)+20)$ Indirect Scaled offset [Access the register, add scaled offset(20) and get the data from the memory location]
It's debatable if Indirect Scaled offset is really even a thing, but considering yet another fact that there's generally no use of offset in Register Addressing, we conclude the best answer is $option\;D$