The same two letters, in the same, consecutive order, will change the words below into two proper nouns and three common words.

TUNA
MAID
OWN
ANEW
ONE

Answers:

The letters DR can either precede or be inserted in each word:

TUNDRA
MADRID
DROWN
ANDREW
DRONE

Credit: LA Times Crossword
Sylvia Bursztyn and Barry Tunick
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