pourity

Question
I have lab of 4 months his hght is 1.7 feet but very sleem.His tail ivery long then his mother. he eats 6chapaties and 1/2L milk and milk bones. he seemes to be mix breed is he.

Answer
Height is taken at the shoulders.  If he is nearly 2 feet at the shoulders the dog is very big already.  Here in the USA we do not give our dogs milk because they do not digest it well, and that could be contributing to your dog being too slim.

Also, unless you buy a dog that comes with pedigree papers, there is NO WAY to tell if it's a pure bred dog or not.  

You can have purebred labs that look nothing like their parents.  That's part of genetics.  You can also have badly bred labs that do not look like labs, but with the pedigree papers, you know that they are.  

I would say just enjoy your puppy and not worry about the breed.