Answer:
D) It is called a participle and it functions as an adjective in this sentence.
Step-by-step explanation:
A participle is a is a verb form or a word derived from a verb that functions as an adjective and can also be part of a verb phrase which is used to create verb tenses. It is usually written before or after a noun.
There are two types of participle namely: present and past participle. In present participle ''ing'' is added at the end of the verb to form a present participle. Where as in past participle, ''ed'''is added at the end to form past participle in regular verbs.
There is also the perfect participle which is formed by combining the word ''having'' with a past participle to form the perfect participle. E.g having left, having watched or having stayed.
The word ''flocking'' in the sentence above is a participle that functions an adjective which describes how the eager students gathered at the area with the latest bestsellers.