Legal analysis: the problem of signing before signing, because signing a blank contract will have the legal consequences of authorizing the other party to fill in the blank part of the contract. In the case that the witness's signature in the loan contract is true, the guarantor should bear the guarantee responsibility within the loan scope regardless of whether the loan amount in the loan contract is written by the other party afterwards.

Legal basis: Civil Code of People's Republic of China (PRC).

Article 143 A civil juristic act that meets the following conditions is valid: (1) The actor has corresponding capacity for civil conduct; (2) the meaning is true; (three) does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.

Article 146 A civil juristic act by the actor and the counterpart with false intention is invalid. The validity of a concealed civil juristic act with false intention shall be handled in accordance with relevant laws and regulations.

The contents of a contract are agreed upon by the parties, and generally include the following terms: (1) the name and domicile of the parties; (2) Subject matter; (3) quantity; (4) quality; (5) Price or remuneration; (6) Time limit, place and method of performance; (7) Liability for breach of contract; (8) Methods for resolving disputes. The parties may conclude a contract by referring to the model texts of various contracts.

Article 478 An offer is invalid under any of the following circumstances: (1) The offer is rejected; (2) The offer is revoked according to law; (3) When the acceptance period expires, the offeree fails to make an acceptance. (4) The offeree makes substantial changes to the contents of the offer.