Welcome to the ODK forum, @Bidemi_Adejumo! When you get a chance, please introduce yourself here.
Thanks so much for using the correct tags on the post. It helps us keep the forum well organized! Speaking of organization, the Development category is for posts about the process of building and modifying ODK tools. Form design questions should go into Support, so I'm moving this question there.
Now that we have that out of the way, I can finally answer your question! If you want to go from makes to models to trims, using cascading selects is your best bet.