A
句意：在化学变化中,一种新的物质生成了.
in the case of:
至于…,在……的情况下,就…来说,就……而言,对……而言
It's the kind of story we think of as myth.But in the case of Lincoln,the story is true.
我们把这类故事视为神话,但就林肯来说,这故事却是真实的.
in case:假使,免得
Be quiet in case you wake the baby.
轻点儿,别吵醒婴儿.
in case of:万一,如果,发生
In case of fire,walk quickly to the nearest door.
如果失火,就赶快朝最近的门跑.
D正确形式为in the event of 万一,倘若
In the event of his death,his daughter will inherit the money.
一旦他故去,他的女儿将会继承这笔钱.
从用法上来说,B是连词,先排除.在ACD中,可根据意思排除CD.
这句话表面意思是：
就化学变化而言,一种新物质生成了.
显然是解释什么是化学变化的,所以给它引申为以上句意.