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.

如图是一辆汽车做直线运动的x-t图象，下列说法正确的是（　　）

A．汽车在OA段运动最快

B．汽车在AB段做匀速直线运动

C．汽车在0～4h内的位移大小为60km

D．汽车在CD段的运动方向与BC段的运动方向相反