单选题 .  As protector of her family's health, the pioneer woman confronted situations she never imagined before crossing the Mississippi. Few women came West prepared to deal with desert sunburn, rattlesnake bites, or arrow wounds. Even when doctors were available, they were often no more knowledgeable than their patients. And most patent medicines were no more reliable than the traveling merchants who sold them.
    In certain cases, a woman could draw upon the folk wisdom and remedies she had learned back home. Western mosquitoes, for example, proved to be as repelled by a paste of vinegar and salt as were their Eastern cousins. More often, however, a woman was guided only by her own skill in preparing tonics, powders, poisons, and polishes from whatever she had at hand: salt made a passable toothpaste; gunpowder was applied to warts, and turpentine to open cuts; goose grease, skunk oil, and the ever-present lard (猪油) were basic liniments (擦剂); medicinal teas and tonics were made from sunflower seeds and roots.1.  According to the passage, why were doctors in the West sometimes unable to help their patients? ______