What do the following three-letter words have in common?

1. ALL

2. BUS

3. DEN

4. THE

5. WAR

 

HINT:

The answer involves the same letter.

 

Answer:

 

The letter Y can be added to each word to make a new one:

 

1. ALLY

2. BUSY

3. DENY

4. THEY

5. WARY 

 

Credit:

Scott Erdman