Warner is among cautious about give the money he purchase , on time.

In the sentence, the preposition 'among' is incorrectly used in place of an adverb which has to qualify/modify the adjective 'cautious', the verb 'give' requires to be in -ing form so that it gives a complete meaning and the verb 'purchase' is contextually irrelevant because the sentence talks about money and it cannot be purchased like other commodities. In option (b), the adjective 'strict' is suggested in place of an adverb. So, the option does not fit into the sentence and gets negated. In option (c), 'irritant' is a noun, suggested in the place of a verb and in option (d), 'illustrate' is a verb, suggested in the place of an adverb. Thus, these two options too do not fit into the sentence and thus get negated. In option (a), the adverb/adjective 'very' ['adverb' here] qualifies the adjective 'cautious', the verb 'returning' which means 'give, put, or send (a thing) back to a place or person' denotes the action done by the subject in -ing form and the verb 'borrowed' which means 'take and use (money) from a person or bank under an agreement to pay it back later' correctly defines the action with respect to the context of the sentence. This option fits into the sentence contextually and grammatically. Hence, the correct answer is option (a).