fathom out . try to discover or devise（an explanation，）寻找解释；找出原因；计算出；推测出

Don't tell me the answer；let me try to fathom it out for myself．别告诉我答案，让我自己设法解答。

The problem was so difficult that it took several days to fathom out an answer．那道题太难，解了好几天才找出答案。

I just can't fathom out his intentions．我就是揣摩不透他的意图。

Can you fathom out where he's gone？你能猜出他到那儿去了吗？

favor with  . do something for somebody as a favour为（某人）特意做（某事）

Mr．Green will now favour us with a song．格林先生将为我们献上一首歌。

 fatten up . give a person or animal plenty to eat，causing him or it to gain weight长肥；养壮

The pigs are being fattened up for market．这些猪正在被催肥待售。

She is fattening up the ducks．她正在把鸭子养肥。

I'm trying to fatten him up as fast as I can．我在努力尽快把他养得壮实些。

fawn on . fawn upon . flatter slavishly； ingratiate oneself with奉承；讨好

One should neither fawn upon those above him nor scorn those below him．人决不可媚上骄下。

She fawns upon anyone with influence．谁有影响力，她就巴结谁。

I don't like Toby， as he always fawns on the rich．我不喜欢托比，因为他老是向有钱人献殷勤。

Don't try to win his support in that way， he hates to be fawned on．不要试图用那个办法赢得他的支持，他讨厌别人奉承他。

 fear for . worry about为…担心；害怕

All mothers fear for their children when they first leave home．天下母亲都为初次离家的孩子担心。

The doctor said，“There's no need to fear for him．He is going to get well．”医生说：“不必为他担忧，他的病会好的。”

We feared for his health．我们为他的健康而担忧。

feast one's eyes upon . feast one's eyes on . look at and enjoy very much饱眼福；很是欣赏

Foreign visitors feasted their eyes on the beautiful scenery in Hangzhou．外宾们饱览杭州的秀丽风景。

He feasted his eyes on the beautiful painting．他很欣赏这幅美丽的画。

They feasted their eyes on the ancient structures in this city．他们用赞美的眼光观赏了这座城市的古老建筑。

 feather in one's cap . something to be proud of； an honor值得骄傲的事；荣誉

It was a feather in his cap to win first prize．他赢得一等奖，真是件值得骄傲的事情。

It'll be a feather in your cap if you can get an interview with him．你如果能见到他，那将是件值得骄傲的事。

It is no small feather in a man's cap if he has been no worse than his neighbours．一个人如果不比周围人差，那是一件很值得骄傲的事。

feather one's nest . use for yourself money and power，esp．from a public office 营私；饱私囊

He used his position and influence to feather his nest．他利用自己的地位和权势谋取私利。

She may do something for you，but she'll be feathering her own nest at the same time．她会为你做些好事，但同时她会从中捞些好处。

Before liberation，many officials feathered their nests through corruption．解放前，许多官吏通过贪污中饱私囊。

feather one's nest . make one's home pleasant and comfortable；decorate one's house装饰家庭

Furniture stores welcome young couples who want to feather their nests．家俱店很欢迎想装饰房屋的年轻夫妇光临。

fed up with . bored with； at the end of one's patience；tired；depressed 受够了；厌烦；对…厌倦

People get fed up with anyone who brags all the time．人们讨厌老是自吹自擂的人。

I am fed up with his laziness and carelessness．我受够了他的懒惰和粗心。

We are fed up with his grumbling．我们已经听厌了他的牢骚怪话。

I'm fed up with this weather，it's time we had some sunshine．我对这种天气极其厌倦，该出太阳了。

feed back . return as feedback反馈

Teachers should attach importance to what is feeding back from the students．教师们应该对从学生处反馈来的信息给予重视。

The teacher found that nothing was feeding back to him from his students．这位教师发觉学生们对他的讲解毫无反应。

The computer feeds back everything you need to know．计算机反馈你所需要了解的一切事情。

feed back .affect or modify the process that brought it about影响或修改原过程，反过来对原过程起促进作用

A lot of ideas are feeding back from the applied science into the pure science．应用科学的许多概念反过来对理论科学起着促进作用。

feed off . eat one's food from（a place，a dish，）从…取得食物

The guests sat cross legged around a low table and fed off a big plate．客人们围着一张矮桌子盘腿而坐，吃大盘子里的东西。

The pigs fed off the same trough．这些猪在一个食槽里吃食。

feed off .use as a source or supplier of food， materials，energy，以…为食物、材料、能量等的来源

These little bears feed off the leaves of this special tree．这些小熊以这种特殊的树叶为食。

When fresh food and water are not available，the camel can feed off its hum．当得不到新鲜食物和水时，骆驼能以驼峰为养料的来源。

To avoid a power cut，they decided to feed off an alternative generator．为了防止停电，他们决定靠备用发电机发电。

Some bigger newspapers feed off reports in smaller papers．一些大报常采用小报的新闻报道。

feed on . feed upon . live on； take as food以…为食物

Cattle feed chiefly on grass．牛主要以草为食。

What do you feed your dog on？你用什么喂你的狗？

We feed our dogs on fresh meat．我们用新鲜的肉喂狗。

He is out of employment and feeds on a friend．他失业了，靠朋友生活。

feed on . feed upon . become nourished，satisfied or strengthened from；consume or utilize from从…得到供养、满足、增强；以…为能源

His convictions feed on determination．由于有了决心，他的信心增强了。

The eye feeds on beautiful objects．美景悦目。

The gas turbine feeds on the fuel it pumps．燃气轮机以它抽入的燃料为能源。