No ambitious politician will challenge an

问题：

No ambitious politician will challenge an elected public official running for reelection unless that official appears vulnerable. Nonetheless, elected public officials who do not appear vulnerable as they attempt to win reelection rarely run unopposed.
If the statements above are true, which of the following conclusions can be properly drawn from them

A．If an elected official running for reelection appears vulnerable, that official’s challengers will all be ambitious politicians.

B．Some elected officials running for reelection are challenged by people who are not ambitious politicians.

C．Elected officials running for reelection who do not appear vulnerable are themselves ambitious politicians.

D．A person who is not an ambitious politician cannot win an election contested by the current officeholder.

E．(E) A politician’s career will be seriously set back if the politician wages an unsuccessful campaign for elective office.