题目解析：
【题目翻译】：根据第5段，一旦太阳处于“后核”阶段，外部区域将与内部区域不同，因为外部区域将有以下哪些情况发生？
A：经历一个不太大的变化
B：保持更接近恒定的温度
C：不再是能量生成活动的场所
D：仍含有一定量的氢
【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。
【关键词定位】：题干中的关键词“postnuclear”, 定位到第五段第1句，说一旦太阳进入“后”阶段，事实上它就会分为两个部分：内部和外部。而下文内容都是在阐述内区和外区所发生的变化。第2句接着说“While no more hydrogen fuel will remain in the inner zone, there will be a small amount left in the outer zone.”这句话其实就包含了内区和外区的一个区别，即内部不再含有氢，而外部仍留有少量的氢。
【逻辑分析】：D选项表明一旦太阳处于“后核”阶段，外部区域将与内部区域不同，因为外部区域将仍含有一定量的氢与关键词所在句子意思相同。
【选项分析】：
D选项：外区仍含有一些氢元素。正确。再来看其他选项为什么错
A选项：外部的体积变化更小。第五段说“The outer envelope will then grow rapidly, increasing, in a short interval, hundreds of times in size.” 恒星的外层会迅速成长，在很短的时间内，体积就会增加数百倍。由此可见，外部的体积变化其实是很大的，但是文中并没有对内外部分的体积变化做具体的对比，所以不管怎么说A选项都是错误的。
B选项：外部的温度会更稳定。错误，因为我们找到这句话“As it expands, it will cool down by thousands of degrees.” 当它膨胀时，它的温度会下降几千度。可见温度变化之剧烈，所以B选项与原文矛盾，故排除。
C选项：停止产生热量。错误，因为文中提到“The inner zone, its nuclear fires no longer burning, will begin to collapse under the influence of its own weight”由此可见能量是在恒星内部产生的，在“后”阶段，恒星的内核会不再燃烧，而不是外部。所以C选项错误。
Once the Sun passes into its "postnuclear " phase, it will separate effectively into two different regions: an inner zone and an outer zone. While no more hydrogen fuel will remain in the inner zone, there will be a small amount left in the outer zone. Rapidly, changes will begin to take place that will serve to tear the Sun apart. The inner zone, its nuclear fires no longer burning, will begin to collapse under the influence of its own weight and will contract into a tiny hot core, dense and dim. An opposite fate will await the outer region, a loosely held-together ball of gas. A shock wave caused by the inner zone's contraction will send ripples through the dying star, pushing the stellar exterior's material farther and farther outward. The outer envelope will then grow rapidly, increasing, in a short interval, hundreds of times in size. As it expands, it will cool down by thousands of degrees. Eventually, the Sun will become a red giant star, cool and bright. It will be so large that it will occupy the whole space that used to be the Earth's orbit and so brilliant that it would be able to be seen with the naked eye thousands of light-years away. It will exist that way for millions of years, gradually releasing the material of its outer envelope into space. Finally, nothing will be left of the gaseous exterior of the Sun; all that will remain will be the hot, white core. The Sun will have become a white dwarf star. The core will shrink, giving off the last of its energy, and the Sun will finally die.
