Serious consideration or reviewing

"Deliberate," "ruminate," and (if you don't need a one-word synonym) "mull over" are all applicable.

Deliberate:

Engage in long and careful consideration. [Lexico]

Ruminate:

Think deeply about something. [Lexico]

Mull over:

To think carefully about something for a period of time. [Cambridge]

Note: please review the links I added to the definitions to familiarize yourself with their specific syntax (e.g. if they are used with prepositions).