Dear Glasguensis：Note that answer A is also perfectly valid : if this is supposed to be a question where only one answer is correct it has been poorly designed
Thank you!Answer B is the one that the questioner wants. The continuous form of the verb allows two actions at the same time - a completed action (the simple form) and an incomplete action (the continuous)
Technically, C is correct also, but this uses the historical future. The historical future is used to bring immediacy to the sentence. It is formed by moving the verbs one tense forward (i.e. towards the future.) However, the historical future is not usually taught to students until they are quite advanced.