The Cloud Natural Language API offers a pre-trained machine learning model capable of performing entity analysis, among other natural language processing tasks. Its Entity Analysis feature can automatically identify and extract relevant subject labels from text, providing a swift and straightforward solution that doesn't require additional development or machine learning expertise. Sentiment Analysis (Option B) focuses on the text's tone and may not be ideal for generating subject labels. Options A and C involve developing and training a text classification model with TensorFlow, which may not be practical given the constraints of limited developer resources and the urgency to implement the feature quickly.