documentclass{article}
usepackage{linguex}
begin{document}
ex. Koitu-wa kamo-des-u\
this-Top duck-Polite-Pres\
``This is a duck.''par % par or one BLANK LINE
ex.  a. Koitu-ra-wa kamo-des-u\
this-PL-Top duck-Polite-Pres\
``These are ducks.''
b. Demo, aitu-ra-wa gan-des-u\
however, that-PL-Top goose-Polite-Pres\
``However, those are geese.''par
ex. Foopar
end{document}