first in first out的first与in分别是形容词与介词?

first in first out的first与in分别是形容词与介词? The message first comes in and first goes out . at first /first/ in first / firstly的差异? find out first 的意思In most places,you don't have to take a gift to a party--but find out first!这句话中的find out first （这篇文章是西方社交礼仪的） LiuXiang came out ___ in the 110-meter hurdlesA.the first B.first为什么选B first first first first first first first “first First First first first first