Which of these would have been a fitting subject for a futurist painting A. a leaf floating down a stream
B. a still life of fruit
C. a fast-moving train
D. a landscape at night

C. A fast-moving train

Explanation:

Because every other answer has to do with nature, they aren't technological and updated like trains. Trains are man-made and are being made better over time, so they can represent a futuristic painting.

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.