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

RAIN
HOST
ABLE
LAND
OWNS

2. What do the following words have in common?

OF
FIT
TON
TEST

HINTS
1. Each word can be preceded by the same letter.:
2. Each word can be preceded by the same three letters.

Answers:

1. Each word can be preceded by G to form a new word:

GRAIN
GHOST
GABLE
GLAND
GOWNS

2. Each word can be preceded by PRO to give a new word:

PROOF
PROFIT
PROTON
PROTEST