a bead of sweat的用法和样例：
- Pete felt a bead of sweat trickle down his face.
- A big bead of sweat rolls down from his forehead.
- Victor's appearance startled the Priest;the boy was extremely pale and disheveled, a bead of sweat on his trembling upper lip, breathing heavily, almost panting.
- Beads of sweat stood on his forehead.
- Beads of sweat rained down his cheeks.