Yeahh.. the question asks which one is a central , front or back vowel?? I cannot give appropriate answer.. what is the difference between them that is how i can distinguish three��
The answer to your question would be quite complex if you wanted to know exact details. However, in a nutshell:
Depending on positioning of the tongue when forming vowels, there are 3 general terms for those types of vowels:
Front, central and back vowels. As the names suggest, when the tongue is positioned in the front of the mouth to form specific vowels, then we refer to those vowels as 'front vowels'. When the tongue is positioned in the middle, it's a central vowel etc.
I hope I may paste a link to the IPA Vowel chart here, which will explain this in more detail: