How did the death of Candy's dog foreshadow what would happen to Lennie in chapter 6 "Of Mice and Men"?

a
Candy's dog is killed cruelly, just as Lennie is at the end of the story.
b
Candy's dog is killed out of mercy, just like Lennie is.
c
Carlson kills Candy's dog and later on kills Lennie.
d
Steinbeck shows that people who are not useful should be killed.

b

Candy's dog is killed out of mercy, just like Lennie is.