Correct option is A
The correct substitution of the highlighted words is (a) cost money and require.
Explanation:
The given sentence is not complete (it lacks a finite verb).
“Books costing money and requiring the user...” is a fragment, not a full sentence.
To make it grammatically correct, we need finite verbs — "cost" and "require".
Thus, the sentence should be: "Books cost money and require the user to read them for the idea to spread."
Grammatical rule used:
Use of finite verbs in independent clauses.
A sentence must have at least one subject and one finite verb to be complete.
Example:
Incorrect: Books costing money and requiring the user...
Correct: Books cost money and require the user...
Booster Tip:
Non-finite verbs like costing and requiring cannot function as main verbs unless they are part of a clause introduced with proper auxiliaries.