The correct answer to complete the sentence is:
b. entró
Explanation:
1. The sentence is in the past tense (preterite form), indicating an action that happened and was completed in the past.
2. The verb "entró" is the preterite form of the verb "entrar" (to enter) in Spanish, which correctly matches the past tense context of the sentence.
3. Therefore, the correct completion of the sentence would be "Después, él entró en la oficina del señor Gomez."