Select the option that expresses the given sentence in active voice.

The library building was renovated in 2020.

They renovated the library building in 2020.

The correct option that expresses the given sentence in active voice is They renovated the library building in 2020.

The other options are incorrect because:

• They were renovating the building in 2020 is in the present progressive tense, while the original sentence is in the past tense.
• They had renovated the library building in 2020 uses the past perfect tense, which is not typically used for actions that happen once.
• They did renovating the building in 2020 is grammatically incorrect. The verb "renovating" is in the present participle form, which is used in the progressive tenses. However, the sentence is in the simple past tense.