time is running out before they will have to retreat to the south.被迫向南迁徙的日子正在一步步逼近

run out:用尽；耗尽；期满

The lease on our flat runs out in a few months.

我们公寓的租约还有几个月就到期了。

My passport has run out.

我的护照已失效。

retreat:撤退；改变；退避

The soldiers had to retreat when they were beaten in battle.

士兵们在战斗中受挫，不得不撤退。

You can't retreat from the responsibility in this affair.

你不能回避在这一事件中的责任。

常用短语:

retreat from (v.+prep.)
1.从…撤退move back from a position or danger

The defeated army had to retreat hastily from the field of battle.

败军被迫仓皇地从战场上撤退。

2.避开…move away from or try to get rid of sb/sth

You cannot retreat from your responsibility in this affair.

你不能回避在这一事件中的责任。

red and yellow pigments build up in their leaves.红色素和黄色素染上了叶子

build up:逐步增长；积累

The company has built up a large fund for ages.

多年来这个公司已积累了大量资金。