请教大全前30题中的几个问题

kimpak

6. A fire in an enclosed space burns with the aid of reflected radiation that preheats the fuel, making ignition much easier and flames spreading more quickly.
(A) flames spreading
(B) flame spreads
(C) flames are caused to spread
(D) causing flames to spread
(E) causing spreading of the flames
答案是D，我选A， 我觉得A可以理解成一个名词短语，这样就可以同前面的ignition平行。如果选D，又作何解释？

12.A little under a million years ago, the briny waters of the Baltic Sea began flooding into the cold North Atlantic: geologists are still debating whether the flood was gradual or created a cataclysm.
(A) whether the flood was gradual or created a cataclysm
(B) if the flood was gradual or created a cataclysm
(C) about whether the flood was gradual or cataclysmic
(D) whether the flood was gradual or cataclysmic
(E) whether the flood was gradual or it created a cataclysm
答案是D，为什么不能选C，我认为C中debateing后接about是固定搭配呀！它与D又区别何在？

18.A peculiar feature of the embryonic mammalian circulatory system is that in the area of the heart the cells adhere to one another, beating in unison and adopting specialized orientations exclusive of one another.
(A) beating in unison and adopting
(B) they beat in unison while adopting
(C) beat in unison, and adopt
(D) beating in unison yet adopting
(E) even though they beat in unison and adopt
答案是D，我选E。只是从语感上觉得E是答案。不知哪位大牛能帮我解释一下。

gemj

18
beating in unison yet adopting
是意思相反的两个状语修饰adhere。

kimpak

33. A substance derived from the Madagascar periwinkle, which has proved useful in decreasing mortality among young leukemia patients, is cultivated in China as part of a program to integrate traditional herbal medicine into a contemporary system of health care.
(A) A substance derived from the Madagascar periwinkle, which has proved useful in decreasing mortality among young leukemia patients,
(B) A derivative, which has proved useful in decreasing mortality among young leukemia patients, of the Madagascar periwinkle,
(C) A Madagascar periwinkle derivative, which has proved useful in decreasing mortality among young leukemia patients,
(D) The Madagascar periwinkle has a derivative which has proved useful in decreasing mortality among young leukemia patients, that
(E) The Madagascar periwinkle, a derivative of which has proved useful in decreasing mortality among young leukemia patients,
答案是E，我的答案是C。我不明白的是这道题到底在考a substance derived from the Madagascar periwinkle被证明是有用的，还是Madagascar periwinkle是有用的？我个人认为C也应该没有错吧，请大牛们赐教！


47.According to scientists at the University of California, the pattern of changes that have occurred in human DNA over the millennia indicate the possibility that everyone alive today might be descended from a single female ancestor who lived in Africa sometime between 140,000 and 280,000 years ago.
(A) indicate the possibility that everyone alive today might be descended from a single female ancestor who
(B) indicate that everyone alive today might possibly be a descendant of a single female ancestor who had
(C) may indicate that everyone alive today has descended from a single female ancestor who had
(D) indicates that everyone alive today may be a descendant of a single female ancestor who
(E) indicates that everyone alive today might be a descendant from a single female ancestor who

答案是D，为什么不是E，一般来讲原句中出现的情态动词不能随意改动呀。这道题中的might,怎么D中就成了may了？