Well if you think about the other possibilities: 1. makes no sense grammatically or logically. 2. could be a sentence grammatically but makes no sense logically (IT does not seem to refer to anything). This sentence COULD be correct under a very specific context. It would have to be something like: The MAGNUS TEMPORA, written in 1470 records many early attempts at clock making. The first clock it recordered . . . . (in this case, we would know what IT refers to). 3. could be a sentence grammatically, but doesn't work logically. It implies that the clock historically recorded something, but doesn't say what it is. At any rate, this is not the intended meaning of the sentence. 4. This is the only answer that works grammatically and makes logical sense. This is a fairly common grammatical structure: The first clock to be recorded. The first student to be honored. The first dog to be fed. The first game to be lost.