1. What do the following two-letter words have in common?

AD
AT
ON
OF

2. What do the following words have in common?

SNOW
BLACK
JAIL
BLUE

Answers:

1. Each word changes into a new one when preceded by GO:

GOAD
GOAT
GOON
GOOF

2. Each word can be followed by BIRD.

SNOWBIRD
BLACKBIRD
JAILBIRD
BLUEBIRD