Sentence:  The best way to determine the correct figure ( in captives ) is by direct observation of pairs isolated from birth , a method that produced surprising results : maturing of a male Indian python in less than two <WSD>years</WSD> , his mate in less than three ; data on the boa constrictor about match this . 
Meaning of the word marked with <WSD> tags:  a period of time containing 365 (or 366) days