作副词用.
for example:
Three factors are attributed to his success:firstly,he works very hard;secondly,...;thirdly,...
他的成功可以被归结为三个因素：第一,他努力工作；第二.
作副词用.
for example:
Three factors are attributed to his success:firstly,he works very hard;secondly,...;thirdly,...
他的成功可以被归结为三个因素：第一,他努力工作；第二.