单选题 . ①The recently announced discovery of the first known planet orbiting a pulsar (the ultradense, pulsating remnant off the supernova explosion of a star) turned out to be based on faulty data. ②Had this discovery been confirmed, theorists would have had difficulty accounting for the existence of such a planet. ③The supernova would certainly have destroyed any preexisting planets. ④This particular pulsar is relatively young, allowing little time for a new planet to have coalesced, and it rotates relatively slowly, implying that it has not interacted with any nearby star since the supernova.
①But newer evidence of a different pulsar with planets is more promising. ②This is a rapidly spurring ''millisecond pulsar" thought to be a much older object that has pulled gaseous material from a stellar neighbor, causing its rotational speed to increase. ③Leftover, unconsumed gas around such a pulsar could, in theory, coalesce into planets. ④Or the pulsar's radiation might have vaporized a companion star, providing new material for planetary formation.4. The primary purpose of the passage is to ______

A、 provide an example of the dangers of a recent discovery based on faulty data.
B、 illustrate the difficulty of explanation concerning a recent discovery
C、 assess the credibility of recent findings concerning the as yet unverified existence of a class of objects.
D、 argue that a certain hypothesis fails to account for a seemingly contradictory phenomenon
E、 demonstrate how difficult it might be to find out the reality of a phenomenon

【正确答案】 C

【答案解析】 C：a class of objects指的是围绕脉冲星的行星。文章第一段否认了这种行星的存在，第二段又肯定了行星的存在，既有加强又有削弱，对应assess，因此选项C正确。
A：文中没提dangers。
B：a recent discovery只对应第一段，没提第二段。
D：本文两段其实分别描述了两个现象，一个是没有行星，一个是有行星。
E：difficult与本文无关。