The question tests the understanding of sentence structure, specifically the use of 'sb.' in the phrase 'allow sb.to do sth.'. The subject in this context is the entity that is being allowed to do something. In the given phrase, 'sb.' refers to both SpaceX and the astronauts aboard the station, making the entire phrase the subject. Option A and B are incorrect because they only refer to parts of the whole subject. Option C is incorrect because the station is not the subject being allowed to do something, but rather a location where the astronauts are aboard.