The passage presents specific details, and comparing them with the choices confirms that "定期的に洗わないと不衛生になることがある。" is the only accurate representation of the text. This is directly supported by the sentence "また、エコバッグの中に肉や魚の汁がこぼれたりすると、菌が繁殖して不衛生になることもあります". To solve info-retrieval or detail-oriented questions, scanning for keywords from the question and mapping them to the options is key. The other choices, such as "肉や魚は絶対に入れないほうがいい。" and "洗剤を使うとエコバッグが壊れてしまう。", introduce incorrect facts or make assumptions unsupported by the passage.