[求助]GWD-3-40

Q40:
Two centuries ago, Tufe Peninsula became separated form the mainland, isolating on the newly formed Tufe Island a population of Turfil sunflowers. This population’s descendants grow to be, on average, 40 centimeters shorter than Turfil sunflowers found on the mainland. Tufe Island is significantly drier than Tufe Peninsula was. So the current average height of Tufe’s Turfil sunflowers is undoubtedly at least partially attributable to changes in Tufe’s environmental conditions.

Which of the following is an assumption on which the argument depends?

There are no types of vegetation on Tufe Island that are known to benefit from dry conditions.

There were about as many Turfil sunflowers on Tufe Peninsula two centuries ago as there are on Tufe Island today.

The mainland’s environment has not changed in ways that have resulted in Turfil sunflowers on the mainland growing to be 40 centimeters taller than they did two centuries ago.

The soil on Tufe Island, unlike that on the mainland, lacks important nutrients that help Turfil sunflowers survive and grow tall in a dry environment.

The 40-centimeter height difference between the Turfil sunflowers on Tufe Island and those on the mainland is the only difference between the two populations.

大家都认为：原来的岛和原来的大陆没有分离时是一样的后来分离了，现在的岛比现在的大陆矮了  是因为两种原因  1.岛变矮了  大陆没有变 2.岛没变大陆变高了
所以c选项取非后是：大陆变高了  即第2种原因（岛没变大陆变高了）    那么原文changes in Tufe’s environmental conditions→the current average height of Tufe’s Turfil sunflowers  即第1种原因（岛变矮了  大陆没有变）  一定推不出来  所以c正确
可是我认为：岛比大陆矮了是有5种原因 1.岛变矮了，大陆没有变  2.岛没变，大陆变高了  3.同时都变高  4.同时都变矮  5.岛变矮，大陆变高只要相对变化幅度相差40就行了
所以c选项取非后是：大陆变高了  即第2种原因或者第3种原因又或者第5种原因    那么原文changes in Tufe’s environmental conditions→the current average height of Tufe’s Turfil sunflowers  即因为岛的环境变化导致现在岛上的高度依然可以由于第3或第5种原因，让原文推理成立啊  那说明c不是assumption
请大家指正啊，我也不知道我的想法对不对？我觉得此题没有答案，没有一个是assumption。