Can you match each of the clues below to one of the choices that follow, and explain the relationship?

1. Butterfly tractor
2. Deering over
3. Unspotted sheep
4. Lion reporter
5. Pal Kangaroo
6. Billy the Goat

CHOICES:
a. Newspaper rookie
b. Notorious frontier outlaw
c. Heavy-duty farm machine
d. Playing the toady
e. Biblical symbol of purity
f. 1957 Rodgers & Hart musical

Answers:

1 - c: Heavy-duty farm machine 
2 - d: Playing the toadie
3 - e: Biblical symbol of purity
4 - a: Newspaper rookie
5 - f: Rodgers &  Hart musical
6 - b: Notorious frontier outlaw

Explanation: Each clue contains the name of a "grown up" animal whose name when young is used to describe it - as suggested by the choices:

Newspaper rookie - Cub reporter
Notorious frontier outlaw - Billy the Kid
Heavy-duty farm machine - Caterpillar tractor
Playing the toadie - Fawning over
Biblical symbol of purity - Unspotted lamb
1957 Rodgers & Hart musical - Pal Joey

Credit: NY Times Crossword
January 9, 1994
Mel Rosen
ALL GROWN UP 

Note: See also I KNEW THEM WHEN.