未经双方书面同意并签字，对本协议的任何变更和增加均无效。

All changes and additions to this agreement are valid when performed in writing and signed by both parties.

youdao

未经双方书面同意并签字，对本协议的任何变更和增加均无效。

All changes and additions to this agreement are valid when performed in writing and signed by both parties.

youdao