Fill in the blank with a suitable pronoun:
_______ is raining heavily.
The subject pronouns can be divided into two general categories – Personal and impersonal pronouns. A personal pronoun is a pronoun that is associated with a particular person, like ‘he’, ‘she’ and ‘they’. While an impersonal pronoun is used to speak about inanimate objects/things. ‘It’ is an impersonal pronoun that is used for this purpose. In the given sentence the verb 'raining' is an impersonal one that doesn’t refer to an action that a person performs. In such case ‘it’ is used as the subject. Thus option C is correct. On the other hand, ‘he’, ‘she’ and ‘they’ cannot be used because they are personal pronouns that are used to denote a person, which is not the case here. Thus options A, B, and D are incorrect.