Several invoices showed the same unexplained charge, so the auditor investigated it. Complete with the correct past-tense phrasal verb based on look, using it to refer to the charge: She ___ immediately.

Բացատրություն

Investigating the unexplained charge is expressed by look into, so its past form fits the auditor's response. Looking it over would mean examining it quickly, which is weaker than the deliberate investigation stated here.