His expression became increasingly sombre...是什么意思？

His expression became increasingly sombre...

他的表情变得越来越严肃。

his

pron. (he的所有格)他的，(he的物主代词)他的东西；det. 属于他的，用于名词前，自己的，指某人的，上帝的；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

expression

n. 表现，表示，表达，表情，脸色，态度，腔调，声调，[数]式，符号，词句，语句，措辞，说法；

例句
He mistakenly ascribes the expression 'survival of the fittest' to Charles Darwin.
他错误地认为“适者生存”是查尔斯·达尔文说的。

became

v. 变为，成为（ become的过去式 ）；

例句
It became very clear that the incident was not just an aberration, it was not just a single incident.
事实已经很清楚，这件事不是偶发的，它并不是一起孤立的事件。

increasingly

adv. 越来越多地，日益，格外，越来越…，愈；

例句
Theirs had been an increasingly attenuated relationship.
他们的关系日益冷淡。

sombre

adj. 忧郁的，昏暗的，阴沉的，暗淡的，不鲜艳的（颜色等）；

例句
The next day dawned sombre and gloomy.
第二天拂晓时，天色阴沉昏暗。