what is the only way to know for sure what a verb stem changes to?\n\nguess.\nno tengo ningún…

Brief Explanations:

In linguistics and language learning, particularly with Spanish "boot verbs" or stem-changing verbs, there is no consistent spelling rule that dictates which verbs will undergo a change (such as $e \rightarrow ie$, $e \rightarrow i$, or $o \rightarrow ue$). Because these changes are irregular and based on the historical evolution of the language rather than predictable patterns, learners must commit each specific verb's conjugation to memory to ensure accuracy.

Answer:

Memorize it!