1. What do the following words have in common?

RODE
COAT
IDES
CRIME
ROME

2. What do the following words and partial words have in common?

EN
SUL
PAL
PAN

3. What do the following words have in common?

STOCK
POCKET
SNORE
GROVEL
OBJECT

HINTS:
1. It has to do with the number of syllables.
2. Each word can be followed by the same three letters.
3. The same change can be made to the same letter in each word. 

Answers:

1. They are one-sylllable words which change into three-syllable words by the addition of a single vowel.

RODEO/COATI/IDEAS/CRIMEA/ROMEO

2. Each word or partial word can be followed by TRY to make a new word.

ENTRY/SULTRY/PALTRY/PANTRY

3. The O in each word can be changed to A to create new words.

STACK/PACKET/SNARE/GRAVEL/ABJECT