When shopping for clothing, you can try the items on in ___ before buying them.

fitting rooms 指「試衣間」，是服飾店或百貨公司內供顧客試穿衣物、確認尺寸或樣式是否合適的空間。題幹的 try the items on（試穿這些商品）與 before buying them（購買前）完全對應此用語。