Concept:The phrase "in time" is a fixed idiomatic expression meaning early enough to do something before it is too late.Explanation:In the given sentence, Frank arrived at the last possible moment and managed to catch the plane.The idiom "just in time" is always used with the preposition "in"."By time", "within time", and "to time" do not form a natural or correct phrase in this context.Compare: "The ambulance arrived just in time to save her."Thus, the missing word that completes the sentence correctly is "in".Answer:D. in