#1 is a grammatical translation, and loses meaning. If you continue to step #3 before attempting to extract meaning from the sentence, it answers your question.

#1 is a grammatical translation, and loses meaning. If you continue to step #3 before attempting to extract meaning from the sentence, it answers your question. There's only one "type" in the reference pool ("the AST type") and, like a list, set, class or tree, it is a collection. Therefore, it is this to which "which" refers.