1. What do the following words have in common?

AIL
ART
ILL
IRE
IRK

2. What do the following words have in common?

AIR
ANT
ARM
EAT
ILL
ORE
URN

Answers:

1. Each word can be preceded by QU:

QUAIL
QUART
QUILL
QUIRE
QUIRK

2. Each word can be preceded by CH:

CHAIR
CHANT
CHARM
CHEAT
CHILL
CHORE
CHURN