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Hello
my Score is 457.Are there any chances of me getting an invitation.?

Not through Express Entry. Either increase your score or look into the Provincial programs.
 
But the score is dropping,So are there any chances it will drop to 457 ?

Are you a CEC applicant? If so, there may be some chance but you should still work to increase your score. Scores are not dropping for FSW applicants.
 
What should we fill in the question where it says when you were eligible to practice this profession?