21. In order to being a good salesclerk, you mustn’t be rude to the customers.
=>be (Vì sau in order to +V1
22. According to the sign on the restaurant door, all dinners are requiring to wear shirts and shoes.
=> required(Vì trong câu cần thì bị động của thì hiện tại đơn nên không dùng Ving mà dùng Ved)
23. My mother always made me to wash my hands before every meal.
=> wash(Theo cấu trúc made (O) V1)

1. The correct sentence is: "In order to be a good salesclerk, you mustn't be rude to the customers." Therefore, the error is in part A ("being"). It should be changed to "be".

2. The correct sentence is: "According to the sign on the restaurant door, all diners are required to wear shirts and shoes." Therefore, the error is in part C ("requiring"). It should be changed to "required".

3. The correct sentence is: "My mother always made me wash my hands before every meal." Therefore, the error is in part C ("made me to wash"). It should be changed to "made me wash".

4. The correct sentence is: "Although his leg was broken, he managed to get out of the car." Therefore, the error is in part B ("however"). It should be removed as it is redundant.

5. The correct sentence is: "The information I got from the assistant was so confusing that I didn't know what to do." Therefore, the error is in part B ("such confusing"). It should be changed to "so confusing".