Remember that in English the subject must always be stated by using a noun or pronoun. I believe it is the same in German and Dutch, but it is not the same in Klingon. In Klingon the absence of a pronoun along with the null prefix (the absence of a prefix) indicates that the subject is either he, she, it, or they. In a real conversation there will usually be plenty of context to make it clear, but on Duolingo, there is often no context and you just have to pick. In this sentence there is a sort of context in that we know that people don't explode, so the thing exploding would be referred to as "it". So you must use "it" with each verb, since English requires some sort of noun or pronoun.