A) They thanked us exuberantly for meeting with them to discuss the deal.
Gerunds are verbs that end in -ing AND are used as nouns in a sentence. The object of a preposition is the last word in a prepositional phrase. The first word of a prepositional phrase is a preposition. Prepositions tell you the relationship of one noun to another. For example, the dog is in the house. In is a preposition telling you where the dog is in relation to the house. House is the object of the preposition. In A the gerund is "meeting" the gerund phrase is "meeting with them" and it is the object of a preposition. The preposition is for. In B, the gerund is "driving". In this sentence, driving is the subject. In C the gerund is memorizing and it is a direct object. In D the gerund is biking, and it is also a direct object.