Unlike other arachnids
, which have their nerve cells evenly
distributed along their <<bodies
, the scorpion's head
has a cluster of nerve cells, as a mammal does.>>
B has 2 errors. First, it implies that arachnids have more than one body. Second it erroneously compares "arachnids" to "scorpion's head" as underlined in red.
C is best and solves for those 2 problems found in B