previous(ly)
1.He wrote to me previous to visiting me等句子里的previous用作副词，习惯上很少用previously。它后面的to是介词，visiting不可改作visit。
2.注意下面第一句里有for，第二句和第三句里都没有for。
- He was the man whom I had studied with for two months previously.
- He was the man whom I had met two months previously.
- He was the man whom I had met the day previously.
3.previously往往跟now相对。例如：They are now friends, but were previously bitter enemies.
