Answer: least
Step-by-step explanation:
Here's the correct question:
Write the correct adverbial form of the word in parentheses.
However, we can ship them _________ expensively by train. (little)
An adverbial is simply referred to as a word which can be used to modify the verb in a sentence or the sentence as a whole.
The correct adverbial form of the word "little" would be "least".