Most gas appliances require routine maintenance once a year to ensure safety.多数煤气用具需要一年一次的定期保养，以确保安全。Besides the annual vacation, one- and two-day holidays scattered throughout the year.除了一年一次的休假以外，全年还有些一天两天的零星假日。My insurance plan covers one complete physical per year.我的保险计划包括一年一次的全身检查。