all at once与all of a sudden有何区别

all at once和all of a sudden均有“突然”的意思，不过前者还有同时的意思。
如：When I asked a question, he put up his hand all at once.
(我一提问，她立刻就举起手)
When I asked a question, she shouted all of a sudden.
（当我提问时，她突然喊了起来）