a.

1. 沒頭腦的
   The handwriting of this scatterbrained fellow was totally illegible.

   這個沒頭腦的傢伙寫的字簡直無法辨認。

2. 注意力不集中的；不專注的
   More often than not, the student was quite scatterbrained.

   絕大部分時候這個學生注意力不集中。