D is the answer that holds up. Sentence A uses "ramshackle" as a noun instead of an adjective, so it can't stand as the correct answer. The writer of that sentence most likely meant to use word "shack." Unless he's a very eccentric millionaire, the guy in sentence B isn't likely to invest his money in a house that might as well be made of cards. Sentence C is shaky too because it uses "ramshackle" as a verb instead of an adjective. The writer was probably searching for the word "shackle," which means "to handcuff." That leaves D and the rickety bridge on the verge of collapse.