Select the option that expresses the given sentence in active voice.
The monkey was not chased up the tree by the lion.

Correct option is B

The correct active voice expression is (b) "The lion did not chase the monkey up the tree."
The passive voice sentence is effectively converted into active voice by placing 'the lion' as the subject and using 'did not chase' as the action that the lion did not perform on 'the monkey.'
Grammatical rule used: In converting from passive to active voice, the agent (the doer of the action in the passive sentence) becomes the subject of the active sentence.
Conversion rule:
Past indefinite
Subject did not + V1 + object. -> <- Object + auxiliary verb (was, were) not + past participle + by + subject.