“观察DNA和RNA在细胞中的分布”实验中，有下列操作：①染色时先用甲基绿染色，再滴加吡罗红；②将涂片用质量分数为8%的盐酸处理后，接着用染色剂染色；③观察时应选择染色均匀、色泽浅的区域；④先用低倍镜找到较清晰的细胞，接着换上高倍镜观察即可。以上操作有错误的是       （添标号）其正确操作为                                             
                                                                                                                                        
                                                                                                                                 。