Put the above four panels in order from the case of easiest input substitutability to the case of the most difficult input substitutability.
Group of answer choices
panel (a), panel (b), panel (c), and panel (d).
panel (a), panel (c), panel (d), and panel (b).
panel (b), panel (a), panel (c), and panel (d).
panel (a), panel (d), panel (c), and panel (b).
panel (d), panel (c), panel (a), and panel (b).