1) recognize...  as
2) recognize sb. /sth. to be _
3) recognize that should+do_
4)I_____Peter by his appearance although I hadn't seen  him for 10 years.虽然我有10年没见彼得了，但是我还是凭  他的外貌认出了他。
5) Liu Xiang____one of the ten first-  class athletes in the world．刘翔被认为是世界上十佳运动员  之一。
6)______that environment pollution has become one of the most serious problems that people face.  人们一致认为环境污染已经成为人们面对的最严重的问题  之一。