配制100mL 1mol/L NaCl溶液，下列操作中错误的是

A．在托盘天平上放两片大小一样的纸，然后将氯化钠放在纸片上称量

B．把称得的氯化钠放入盛有适量蒸馏水的烧杯中，溶解、冷却，再把溶液移入容量瓶中

C．用蒸馏水洗涤烧杯、玻璃棒2～3次，洗涤液也移入容量瓶中

D．沿玻璃棒往容量瓶中加入蒸馏水，直至溶液凹液面恰好与刻度线相切

It is probably easier for teachers than for students to appreciate the reasons why learning English seems to become increasingly difficult once the basic structures and patterns of the language have been understood．