The correct choice is Option 3: 'Explaining products to customers in polite Japanese.' The text states: '特に、お客さんが買いたいものを尋ねてきたとき、丁寧な日本語でどのように説明すればよいか分からず...大変でした' (Particularly, when customers asked about things they wanted to buy, not knowing how to explain it in polite Japanese was tough). This matches Option 3. Options 1, 2, and 4 are irrelevant or not in the text.