she is on --diet,for she is trying to lose weight

go on a diet /be on a diet " 吃某种特殊饮食,节食 ", 这是固定搭配。 You must go on a diet because you are too fat。 你必须限定饮食因为你太胖了。 也有on diet的说法,是由on a diet 省略而来,多用于口语或非正式场合。 It is always not easy to get on diet。 节食减肥却不是那么容易。