O / A (definite article), O / A (definite article for generic references), A (ordinal number), O / A (specificities in context), Esse / Essa (when used for emphasis)
Um (indefinite article), Um (numeral), Uma (feminine form of indefinite article), Expressing a single instance or example, A (preposition, indicating direction), A (indicating a range or type)
Ir, Funcionamento (to work/function), Passar (to go by or to pass), Continuar (to continue or proceed), Acontecer (to happen), Desaparecer (to disappear or to leave)