How to slow down an animation with repeat and auto

问题:

I'm using UIView animateWithDuration. I'm use to UIView beginAnimation but apple says that it's better since iOS4.0 to use the new method.

I have an issue though. I can't slow down the animation I'm trying to have.

[UIView animateWithDuration:25.0f delay:0.0f 
 options:(UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse)    
animations:^
{self.frame = CGRectMake(self.frame.origin.x, self.frame.origin.y,
self.frame.size.width*0.97f, self.frame.size.height*0.97f);} 
completion:nil];

I can change the value of animateWithDuration to what I want it'll always do the same animation !

Thanks for the help