本合同只有经双方当事人授权的代表正式签署的书面文件，方可修改。

This Agreement may be amended only by a written instrument signed by duly authorized representatives of both parties.

youdao

经各方正式授权的代表签字批准，本协议已经生效，特此证明。

IN WITNESS "WHEREOF", the Parties have caused this contract to be effective with the signatory approval of their duly authorized representatives.

youdao

经各方正式授权的代表签字批准，本协议已经生效，特此证明。

IN WITNESS "WHEREOF", the Parties have caused this contract to be effective with the signatory approval of their duly authorized representatives.

youdao