this problem is about tense.
simple present, and present perfect is used frequently and are basic tense. but this dose not mean we master these basic tenses.
it is funny that we master these tenses by reading some explanations of experts who are native speakers. some persons said we do not need to be grammarian to excel on gmat. this is correct. but we do need to master basic grammar points to excel on gmat.
we need to read a grammar book to master the basic points of grammar. we do not need to learn hard and not basic grammar points. gmat test only the basic point of grammar. this is absolutely correct and so, we need to focus on basic points when reading grammar books. so, be careful when you read grammar books.
I Have failed gmat many years. so, I want to give you the helping words.
now, I consider myself too ambitious to make you understand simple tense and present perfect tense with a few lines of words. you need to read a few pages in good grammar books to master these tenses to solve this problem properly
simple tense is used to show an event existing at the moment of speaking or an event exist indefinitely , before, in and after moment of speaking
present perfect is used to connect event past to present time.
those are 2 sentences which will help you learn grammars books.
only present perfect is fit . only choice C is fit
read about tenses in good grammar books. and dont read the not basic points. you yourself find out which points are basic and which points are not