定下来的英文：
finalise
decide
fix

参考例句：

Have they decided on the location of the new Building yet?
这座新建筑的位置你们定下来了吗?

So at that time, China set the keynote for a settlement of the Hong Kong question.
所以，解决香港问题，我们的调子就是那时定下来的

We must peg him dram to a definite date for completion.
我们一定要让他将完成的日子定下来。

Plans for the picnic are still left in the air since we can't decide where to go.
关于出去野餐的计划还悬而未决，因为去哪儿我们还未定下来。

I'll return to Shanghai tomorrow, if I can firm up my air ticket
如果我能把飞机票定下来的话，我打算明天回上海。

finalise是什么意思：
v. 使…结束；把…最后定下来

They finaly said yes.
他们最后同意了。

They met to finalise the terms of the treaty.
他们会晤确定条约的条款。

let's finalise the proposal.
让我们把这个提议定案吧。

decide是什么意思：
v. 决定；解决；裁决；影响…的结果

to decide By lot
抽签决定

They decided to scrutinise.
他们决定认真调查。

The tense used is decided by the subject.
所用的时态取决于主语。

fix是什么意思：
v. 使固定；牢记；修理；安排；操纵；注视
n. 困境；贿赂

Have you fixed on the date?
日期选定了吗?

The horse race was a fix.
这场赛马有人操纵。

Can you get a fix on the submarine?
你能给潜水艇定位吗?