It's MINERAL. and nothing whatsoever to do with steam engines.
If the questions had been phrased "Are they.....?" the answers would have been:
(Boolbar) YES, probably
(Superman) They're probably found in almost every country.
(Raak) Not a work of art.
(Bismarck) Not a monument.
Over to you, Superman.
Now this one is
MINERAL and VEGETABLE and nothing whatsoever to do with steam locomotives.
Without further ado, let me announce an
ANIMAL subject on the card. Listen carefully as the mystery voice reads out the clue.
Well, it's ANIMAL
Your turn again.
The next is MINERAL.
ABSTRACT
(as well as trouble for a few geological theories when it's discovered).
Hint: the connection with light might be the most promising approach.
Right then, the next one is
MINERAL with an ABSTRACT feel
ABSTRACT ANIMAL