Final answer:
A cloud described as bearing 'the coming harvest in its breast' is metaphorically likened to a pregnant entity symbolizing its potential to deliver life-giving rain necessary for a bountiful harvest.
Step-by-step explanation:
When a cloud is described as bearing 'the coming harvest in its breast', it can mean several things, each capturing the cloud's relationship to the impending agricultural yield. Option D provides the clearest metaphor drawn from the given options, likening the cloud to a pregnant entity, symbolizing its readiness to deliver rain essential for nurturing crops. This is akin to how a pregnant being carries the potential for new life.
Clouds, in their capacity to provide rain, carry within them the promise of life for the plants below, which ties into the metaphor of pregnancy where the fruition is both anticipated and necessary for future sustenance. Hence, the cloud symbolizes the abundance of life-giving rain that will ensure a bountiful harvest.