7、Contracts， in law， is an agreement that creates an obligation binding upon the parties thereto.The essentials of a contract are as follows: (1)mutual assents; (2)a legal consideration(法律:约因、对价)， which in most instances need not pecuniary(与金钱有关的); (3)parties who have legal capacity to make a contract; (4)absence of fraud(欺诈，诈骗)or duress(胁迫); and (5)a subject matter that is not illegal or against public policy.In general， contracts may be either oral or written.Certain classes of contracts， however， in order to be enforceable， must be written and signed.These include contracts involving the sale and transfer of real estate(不动产); contracts to guarantee or to answer for(对…承担责任)the miscarriage(不履行合同)， debt， or default(拖欠)of another person， etc.