一般来说,英语中,单独的非主语成分放在句首,大多都【表示强调】.
副词放在句首,也不例外.一般可用于强调某一动作、情况和结果、情绪或层次顺序、重要性等等.例如：
Quickly,they moved along in another direction.【强调moved along 这一动作】
Firstly,you have to believe in yourself.【强调层次顺序、重要性】
Fortunately,the two brothers were saved with the help of the villagers.【强调情况和结果】