question:  Why did Val become so tired during her trek across the desert?
context: The planet itself was tough enough—barren, desolate, forbidding; enough to stop the most adventurous and dedicated. Val's usually about the best wife a guy could ask for, but when she wants to be she can be a real flying bother. But no; she blamed it all on me somehow: So we were out walking on the spongy sand of the Martian desert. When Val's tired and overwrought there's no sense in arguing with her. We had wandered fruitlessly over the red sands all day, both of us listening for the clicks of the counter. Even though the Martian gravity was only a fraction of Earth's, I was starting to tire, and I knew it must have been really rough on Val with her lovely but unrugged legs. She had been just as much inflamed by the idea of coming to Mars to help in the search for uranium as I was. I didn't dare turn up her oxy pressure any higher, but it was obvious she couldn't keep going. I stopped, slipped out of the geiger harness, and lowered myself ponderously to the ground. She slid down beside me, curled up, and in a moment she was fast asleep, sprawled out on the sands. I watched her, sleeping peacefully, a wayward lock of her soft blonde hair trailing down over one eyebrow, and it seemed hard to believe that we'd exchanged Earth and all it held for us for the raw, untamed struggle that was Mars. Val and I helped each other to our feet as best we could, considering our arms were still tightly bound against the sides of our oxysuits. We trudged along together, with him following behind; I could hear the crunch-crunch of the wheelchair as its wheels chewed into the sand. The great atomic wars of the late 20th Century had used up much of the supply, but the amount used to blow up half the great cities of the world hardly compared with the amount we needed to put them back together again.
output:  She did not have the technology that enabled Ron to persist
options:  She did not have the technology that enabled Ron to persist  She became consumed with resentment for having traveled to Mars  She had trouble adjusting to the Martian climate and terrain  Uranium was seeping through her space suit