Owner started feeding the puppy with a special puppy food once the puppy was of 3 months. Here the owner only made changes with food of the puppy, keeping all other conditions constant.
He then recorded his data in the form of table, which could also be plotted graphically. Since his observations included numbers to present information, it can also be called as quantitative observations. However, he did not make use of metric system for recording the observation. A metric system is based on the multiples of 10.
Hence, the correct answer is option (b) the owner used metric system.