to improve a machine, computer system, etc. in terms of efficiency, standards, etc.
升级, 改善
(of a document, contract, etc.) to no longer be legally recognized because of reaching the end of validity period
到期, 失效
problems or difficulties that arise, especially in relation to a service or facility, which require resolution or attention
问题, 困难
to sell more tickets or accept more reservations than the available number of seats, rooms, etc.
超额预订, 过量预订
to formally promise that specific conditions related to a product, service, etc. will be fulfilled
保证, 担保
to make a person remember an obligation, task, etc. so that they do not forget to do it
提醒, 使想起
suitcases, bags, etc. to keep one's clothes and other belongings while traveling
行李, 行李箱
to tell someone in advance about a possible danger, problem, or unfavorable situation
警告, 告知
to provide someone with suggestion or guidance regarding a specific situation
建议, 忠告