If Skill' s book is published this year, Professor Nguyen vows she will urge the dean to promote Skiff. Thus, if Skiff' s book is as important and as well written as Skiff claims, he will be promoted, for Nguyen will certainly keep her promise, and the dean will surely promote Skiff if Nguyen recommends it. The argument's conclusion can be properly inferred if which one of the following is assumed? ['Skiff needs to publish a book before he can be promoted.', "Skiff's book will not be published unless it is as important and as well written as he claims it is.", 'Skiff will not be promoted unless Professor Nguyen urges the dean to do so.', "Skiff's book will be published this year if it is as important as he claims it is."]