and someone comes in from another room with a cake on which
1个回答

and someone comes in from another room with a cake on which are lighted candles one for each year

with a cake 介宾短语作状语.

which指代蛋糕,这里是定语从句.

意思:有人从另一间屋子进来,拿着蛋糕,上面插着蜡烛,一根代表一岁.

The cake is cut in pieces,蛋糕被切成块儿,in pieces不是固定搭配,只是很常见而已.