They cannot just stand by themselves. There is usually only one possibility of preposition which must be used after a particular noun. Occasionally alternatives are possible. But in either event ...

A preposition is a word that tells you where or when something is in relation to something else. Examples of prepositions include words like 'after', 'before', 'on', 'under', 'inside' and 'outside'.

English grammar is the foundation of effective communication ... They must match the noun they replace in person, number, and ...