she is worried about her sick mothershe_____ her sick mothera. is worried aboutb.worries forc.is worrying from为什么答案是A,B错在哪里,C错在哪里?

这个是习惯用法， 多看人家的文章，就出来了。

be worry about 是词组

习惯搭配
be worried about sb./ sth.担心.这里的worried是形容词
B,C的介词搭配不当
另外,可以有 sth.worries sb.
worry做动词,表示使某人担忧

额，虽然我不愿意这么说，但是从小老师告诉我 be worried about 固定搭配~
要是深究的话，worry
及物动词 vt.
1.
使担心,使发愁
Nothing worries me.
我没有什么可担心的。
2.
担心,发愁[Y][+wh-][+(that)]
The teacher worried that these problems might be too hard for her students.
老师担心这些题目会对学生太难。
Don't worry how much you spend on the trip.
别担心花多少钱用于旅行。
3.
使不安宁;骚扰;折磨
For God's sake don't worry me.
看在上帝分上,别使我不得安宁。
不及物动词 vi.
1.
忧虑,担心[(+about/over)]
Don't worry about the matter, take it easy.
别担心那件事,轻松一点。
She worried over her father's health.
她为父亲的健康担忧。