2.

　　【正確答案】：(1)A、B兩個企業簽訂的買賣合同有效。根據《合同法》的有關規定，法人的法人代表人超越權限訂立的合同(包括擔保合同)，除相對人知道或者應當知道其超越權限的以外，該代表行為有效，合同成立有效。在本案中，B企業并不知道A企業的法定代表人張某超越了內部權限，因此張某的代表行為有效，買賣合同成立有效。

　　(1) The sales contract signed by Company A and B is valid. According to the Contract Law, where the legal representative or the person-in-charge of a legal person or an organization of any other nature entered into a contract acting beyond his scope of authority, unless the other party knew or should have known that he was acting beyond his scope of authority, such act of representation is valid. In this case, Company B didn't know Mr. Zhang, Company A's legal representative, was acting beyond his scope of authority. So Mr. Zhang's act of representation is valid. The sales contract is valid.

　　(2)A企業有權在6月5日行使不安抗辯權，中止履行合同。根據《合同法》的有關規定，應當先履行債務的當事人，有確切證據證明對方經營狀況嚴重惡化的，可以中止履行，要求對方提供擔保。

　　(2) Company A has the right to exercise the right of unassured pleadings, and stop fulfilling the contract. According to the Contract Law, the party required to perform first may suspend its performance if it has the conclusive evidence establishing that the other party's business has seriously deteriorated, and demand the other party provide appropriate assurance.

　　(3)A、B兩個企業簽訂的抵押合同有效，但雙方在抵押合同中“如B企業不能支付到期貨款，該廠房的所有權直接歸A企業所有”的約定無效。根據規定，抵押人和抵押權人在合同中不得約定在債務履行期限屆滿抵押權人未受清償時，抵押物的所有權轉移為債權人所有。但該約定內容的無效不影響抵押合同其他部分內容的效力。

　　(3) The mortgage contract signed by Company A and B is valid, but the statement that if Company B couldn't pay for the goods, the machine tools belonged to Company A is invalid. According to the Guaranty Law, the mortgagor and the mortgagee may not stipulate that the ownership of the mortgaged property shall be transferred to the creditor in case the mortgagee's claim is not satisfied after maturity of the debt. But this doesn't affect the validity of other parts.

　　(4)A企業與C企業的分支機構甲簽訂的保證合同是有效的。根據規定，企業法人的分支機構有法人書面授權的，可以在授權范圍內提供保證。甲分支機構已經取得總公司C的書面授權書，因此有權對外提供保證。

　　(4) The guaranty contract signed by Company A and Jia, the branch of Company C, is valid. According to the regulations, if a branch of an enterprise as a legal person has a power of attorney from the legal person, it may provide a suretyship within the scope of authority. The branch Jia has the power of attorney from the Company C, so he can provide a suretyship.

　　(5)根據規定，保證人甲與債權人A未約定保證期間的，保證期間為主債務履行期屆滿之日起6個月。在本案中，主債務的履行期屆滿之日為7月10日，所以保證人C的保證期間為2009年7月10日～2010年1月10日。

　　(5) According to the regulations, if the surety Jia and the creditor A have no agreement on the term of suretyship, the term of suretyship shall be six months from the date of maturity of the principal debts. In this case, the date of maturity of the principal debts is July 10, so Company C’s term of suretyship is July 11, 2009 to January 11, 2010.

　　(6)B企業轉讓機床的行為是不符合《物權法》規定的。根據規定，在抵押期間，抵押人經抵押權人同意轉讓抵押財產的，應當將轉讓所得價款向抵押權人提前清償債務或提存。在本題中，B企業并沒有經過A公司同意便轉讓機床，而且也未將轉讓價款提前清償債務或提存，因此B的轉讓行為不符合法律規定。

　　(6) The action of Company B’s transferring machine tools isn’t in line with the Property Law. Where a mortgagor alienates, upon consent of the mortgagee, the mortgaged property during the mortgage term, the money generated from such alienation shall be used to pay off debts to the mortgagee in advance or be submitted to a competent authority for keeping. In this case, Company B alienated the machine tools, not having the consent of Company A, and the money generated from such alienation shall be used to pay off debts to the mortgagee in advance or be submitted to a competent authority for keeping, so B’s alienation is illegal.

　　(7)甲分支機構拒絕履行保證責任的理由成立。根據規定，在合同約定的保證期間或者法律規定的保證期間，債權人未對債務人提起訴訟、申請裁定的(適用于一般保證)，或者未要求保證人承擔保證責任的(適用于連帶保證)，保證人免除保證責任。在本案中，甲分支機構的保證期間為2009年7月10日～2010年1月10日。債權人A直到2010年6月1日才要求其承擔保證責任，已超出了保證期間，所以甲分支機構的保證責任免除。

　　(7) The reason for Jia’s refusing to perform suretyship liability is reasonable. According to the regulations, where the creditor neither files a lawsuit against the debtor, applies for arbitration(applied to general suretyship), nor demand that the surety undertake suretyship liability(applied to suretyship of joint and several liability) during the term of suretyship agreed in the contract or provided by the law, the surety shall be relieved of the suretyship liability. In this case, Jia’s term of suretyship is July 11, 2009 to January 11, 2010. The creditor didn’t demand the surety undertake suretyship liability until June 1, 2010, beyond the term of suretyship, so Jia is relieved of the suretyship liability.