Final answer:
Option B: In early spring the gardener planted the tomatoes.
Step-by-step explanation:
The sentence that correctly demonstrates the active voice is option B: In early spring the gardener planted the tomatoes.
In active voice sentences, the subject performs the action of the verb. In this case, the subject 'the gardener' is performing the action of planting the tomatoes.
Option A and C are examples of passive voice because the subject 'the tomatoes' is receiving the action of being planted. Option D is also passive voice, and it includes additional unnecessary information about the garden being in early spring.