Fill in the blank with a suitable preposition:
I will be staying in Korea _______ a month.
The given sentence provides the period during which the speaker will stay in Korea. Hence ‘for’ would be the suitable answer, since ‘for’ is used to refer to a duration or period during which an event or action happens. He/she will stay in Korea only for a month and not more than that. Thus option C is correct. On the other hand, prepositions ‘from’ and ‘since’ are used to denote a starting point or beginning of an action, which are not suitable here as the sentence speaks about a well-defined period of ‘a month’. Thus options B and D are incorrect. Whereas ‘on’ is used to denote a day/date or a place which is not the case here. Therefore option A is incorrect.