1·I can't make a definite promise.
我无法作出肯定的承诺。
2·A week ago you made a definite promise.
你一个星期前就满口答应过。
3·They tried to pin him down to a definite promise .
他们试图使他做出明确的保证。
4·We can offer you any of these samples firm for three weeks but cannot promise anything definite beyond that period in view of the heavy demand for this type of goods.
但是，鉴于这一型的商品需求量庞大，超过此期间，就无法明确地承诺。