Sentence:  For example , the marked susceptibility of the monkey to respiratory infection might be related to its delicate , long alveolar ducts and short , large bronchioles situated within a parenchyma entirely lacking in protective supportive tissue barriers such as those found in types <WSD>1</WSD> , and 3 , . 
Meaning of the word marked with <WSD> tags:  used of a single unit or thing; not two or more