the vegetables对的（注意拼写）,如果硬要挑刺儿,可把复数前面的the去掉,不过这又应以上文未提及过为前提.
A good general diet should include plenty of fresh vegetables.
良好的日常饮食应该包含大量的新鲜蔬菜.
有毛病的是倍数表示法,three times后面是缺少东西的.
The price of vegetables is three times higher than that of last year.
The price of vegetables is three times as high as that of last year.
The vegetables are three times the price of last year.（建议此句）
The price of vegetables have increased three times since last year.
以上three times可用triple或threefold替换,而意思不变.
顺便说,2倍一般只能说twice和double,没有说two times、twofold的,也没有说twice/double times的.汉语中的“增加了”几倍,应该先算出总倍数再用英语直接说总倍数,因为英语是不区分“增加了”与“增加到”的.